DOE-HDBK-1092-2004, Electrical Safety
Functional areas: Electrical Energy, National Electric Code, Electrical Safety
The Electrical Safety Handbook presents the Department of Energy (DOE) safety standards for DOE field offices or facilities involved in the use of electrical energy. It has been prepared to provide a uniform set of electrical safety guidance and information for DOE installations to effect a reduction or elimination of risks associated with the use of electrical energy. The objectives of this handbook are to enhance electrical safety awareness and mitigate electrical hazards to employees, the public, and the environment.
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Supersedes:
DOE-HDBK-1092-98, Electrical Safety on Dec 07, 2004
Superseded By:
DOE-HDBK-1092-2013, Electrical Safety on Jul 25, 2013
Version history and related documents
Superseded by
A newer version replaces this document.
- DOE-HDBK-1092-2013Electrical Safety (Jul 25, 2013)
Document text
Text extracted from the attached file. Refer to the original document for the authoritative version.
Section 1
DOE HANDBOOK
ELECTRICAL SAFETY
U.S. Department of Energy AREA SAFT
Washington, D.C. 20585
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
DOE-HDBK-1092-2004
December 2004
Superseding
DOE-HDBK-1092-98
January 1998
NOT MEASUREMENT
SENSITIVE
DOE-HDBK-1092-2004
i
Available on the Department of Energy
Technical Standards Program
Web site at
http://tis.eh.doe.gov/techstds/.
DOE-HDBK-1092-2004
ii
FOREWORD
1. This Department of Energy (DOE) Handbook is approved for use by the Office of
Environment, Safety, and Health and is available to all DOE components and their
contractors.
2. Specific comments (recommendations, additions, deletions, and any pertinent data) to
enhance this document should be sent to:
Patrick Tran
EH-22/270 Corporate Center
U.S. Department of Energy
1000 Independence Ave. SW
Washington DC 20585-0270
3. The DOE Electrical Safety Handbook replaces the DOE Electrical Safety Handbook that
was originally issued in 1998. DOE handbooks are part of the DOE directives system and
are issued to provide supplemental information regarding the Department's expectations
for fulfilling its requirements as contained in rules, Orders, Notices, and regulatory
standards. The handbooks may also provide acceptable methods for implementing these
requirements. Handbooks are not substitutes for requirements, nor do they replace
technical standards that are used to describe established practices and procedures for
implementing requirements.
4. This document contains DOE-developed explanatory material in support of OSHA
regulations and nationally recognized electrical safety related standards and other
information. This document was revised to include a new chapter 11, Electrical Safety
during Excavations, the latest editions of 29 CFR 1910 and 1926, 2002 National Electrical
Code (NFPA 70, 2002), National Electrical Safety Code (ANSI-C2, 2002), Recommended
Practice for Electrical Equipment Maintenance (NFPA 70B, 2002), International Electrical
Testing Association (NETA, 1997), and Standard for Electrical Safety in the Workplace
(NFPA 70E, 2004).
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CONTENTS
FOREWORD................................................................................................................................................. ii
1.0 INTRODUCTION...........................................................................................................................1-1
1.1 PURPOSE..................................................................................................................................1-1
1.2 SCOPE.......................................................................................................................................1-1
1.3 AUTHORITY HAVING JURISDICTION .....................................................................................1-2
2.0 GENERAL REQUIREMENTS.......................................................................................................2-1
2.1 ELECTRICAL MAINTENANCE OR REPAIRS ..........................................................................2-1
2.1.1 WORK ON ENERGIZED/DEENERGIZED ELECTRICAL EQUIPMENT ........................2-1
2.1.2 CONSIDERATIONS FOR WORKING ON ENERGIZED SYSTEMS AND
EQUIPMENT....................................................................................................................2-1
2.1.3. SAFETY WATCH RESPONSIBILITIES AND QUALIFICATIONS...................................2-2
Section 2
2.2 BASIC SAFEGUARDS...............................................................................................................2-2
2.3 RESPONSIBILITIES ..................................................................................................................2-3
2.3.1 MANAGEMENT RESPONSIBILITIES .............................................................................2-3
2.3.2 EMPLOYEE RESPONSIBILITIES ...................................................................................2-3
2.4 REVIEWS/INSPECTIONS .........................................................................................................2-4
2.5 APPROVAL OF ELECTRICAL EQUIPMENT............................................................................2-4
2.6 CODES, STANDARDS, AND REGULATIONS..........................................................................2-4
2.7 GROUND FAULT CIRCUIT INTERRUPTERS AND ARC FAULT CIRCUIT
INTERRUPTERS .......................................................................................................................2-5
2.7.1 HOW A GFCI WORKS.....................................................................................................2-5
2.7.2 USES ...............................................................................................................................2-6
2.7.3 ARC FAULT CIRCUIT INTERRUPTERS ........................................................................2-7
2.8 TRAINING AND QUALIFICATIONS OF QUALIFIED WORKERS ............................................2-8
2.8.1 FORMAL TRAINING AND QUALIFICATIONS ................................................................2-8
2.8.2 TRAINING OF SAFETY PERSONNEL............................................................................2-9
2.9 WORKING SPACE AROUND ELECTRICAL EQUIPMENT......................................................2-9
2.9.1 ELECTRICAL EQUIPMENT RATED AT 600 VOLTS OR LESS.....................................2-9
2.9.2 ELECTRICAL EQUIPMENT RATED OVER 600 VOLTS..............................................2-11
2.10 IDENTIFICATION OF DISCONNECTION MEANS .................................................................2-12
2.10.1 DISCONNECTING MEANS ...........................................................................................2-12
2.10.2 PANELBOARD CIRCUIT DIRECTORIES .....................................................................2-12
2.10.3 ENCLOSURE LABELING ..............................................................................................2-12
2.10.4 LOAD LABELING...........................................................................................................2-12
2.10.5 SOURCE LABELING .....................................................................................................2-12
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2.11 WORK INSTRUCTIONS ..........................................................................................................2-13
2.11.1 SAFE WORK INSTRUCTIONS AND SUPERVISION...................................................2-13
2.12 ELECTRICAL PERSONAL PROTECTIVE EQUIPMENT........................................................2-14
2.12.1 MANAGEMENT'S RESPONSIBILITIES ........................................................................2-14
2.12.2 INSPECTING PPE.........................................................................................................2-14
2.12.3 CLEANING AND ELECTRICAL TESTING OF PPE......................................................2-15
Section 3
2.12.3.1 TESTING ...................................................................................................................2-15
2.12.3.2 TESTING APPARATUS ............................................................................................2-15
2.12.3.3 RETESTED PPE .......................................................................................................2-15
2.12.4 LIVE-LINE TOOLS.........................................................................................................2-15
2.12.4.1 FIBERGLASS-HANDLED TOOLS ............................................................................2-15
2.12.4.2 WOODEN-HANDLED TOOLS ..................................................................................2-15
2.12.5 MAXIMUM USAGE VOLTAGE......................................................................................2-16
2.12.6 MAXIMUM USAGE VOLTAGE FOR LIVE-LINE TOOLS..............................................2-16
2.12.7 RUBBER-INSULATED GLOVES...................................................................................2-16
2.12.8 STORAGE......................................................................................................................2-16
2.12.9 SAFETY SHOES, HARDHATS, AND GLASSES ..........................................................2-16
2.13 WORK PRACTICES.................................................................................................................2-17
2.13.1 TRAINING......................................................................................................................2-17
2.13.1.1 LIVE PARTS ..............................................................................................................2-17
2.13.1.2 SAFE PROCEDURE .................................................................................................2-17
2.13.1.3 CIRCUITS AND EQUIPMENT...................................................................................2-17
2.13.1.4 STORED ELECTRICAL ENERGY ............................................................................2-18
2.13.1.5 STORED NONELECTRICAL ENERGY ....................................................................2-18
2.13.1.6 LOCKOUT/TAGOUT PROCEDURE .........................................................................2-18
2.13.2 VERIFICATION OF DEENERGIZED CONDITION .......................................................2-18
2.13.2.1 VOLTAGE VERIFICATION TEST .............................................................................2-18
2.13.2.2 APPLICATION OF GROUNDS .................................................................................2-19
2.13.3 REENERGIZING EQUIPMENT .....................................................................................2-19
2.13.3.1 TESTS AND VISUAL INSPECTIONS .......................................................................2-19
2.13.3.2 WARNING EMPLOYEES ..........................................................................................2-19
2.13.4.1 APPROACH DISTANCE ...........................................................................................2-20
2.13.4.2 TWO WORKERS.......................................................................................................2-20
2.13.4.4 ILLUMINATION..........................................................................................................2-20
2.13.4.5 SYSTEMS UNDER LOAD.........................................................................................2-20
Section 4
2.13.4.6 WORKING WITH TEST INSTRUMENTS AND EQUIPMENT ..................................2-20
2.13.4.6.1 QUALIFIED EMPLOYEES...................................................................................2-21
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2.13.4.6.2 VISUAL INSPECTIONS.......................................................................................2-21
2.13.4.6.3 RATING INSTRUMENTS AND EQUIPMENT.....................................................2-21
2.13.4.6.4 CALIBRATION OF ELECTRICAL INSTRUMENTS ............................................2-21
3.0 ELECTRICAL PREVENTIVE MAINTENANCE.............................................................................3-1
3.1 DEVELOPMENT AND IMPLEMENTATION REQUIREMENTS ................................................3-1
3.2 DEFINITION...............................................................................................................................3-1
3.3 MAINTENANCE .........................................................................................................................3-1
3.4 INSPECTION .............................................................................................................................3-1
3.5 ESSENTIAL ELEMENTS ...........................................................................................................3-3
3.6 PLANNING AND DEVELOPING AN EPM PROGRAM; FUNDAMENTALS OF EPM...............3-3
3.7 GROUND-FAULT PROTECTION..............................................................................................3-3
4.0 GROUNDING................................................................................................................................4-1
4.1 REGULATIONS, CODES, AND REFERENCES .......................................................................4-1
4.1.1 ENGINEERING SPECIFICATIONS AND DRAWINGS ...................................................4-1
4.2 CIRCUIT AND SYSTEM GROUNDING.....................................................................................4-1
4.3 EQUIPMENT GROUNDING ......................................................................................................4-1
4.4 BONDING...................................................................................................................................4-2
4.5 GROUNDED OR UNGROUNDED SYSTEMS ..........................................................................4-3
4.5.1 GROUNDED SYSTEMS..................................................................................................4-4
4.5.2 UNGROUNDED SYSTEMS.............................................................................................4-5
4.5.3 HIGH-IMPEDANCE GROUNDING..................................................................................4-5
4.6 GROUNDING REQUIREMENTS...............................................................................................4-6
4.7 GROUNDING ELECTRODE CONDUCTOR .............................................................................4-7
4.7.1 SIZING THE GROUNDING ELECTRODE CONDUCTOR..............................................4-8
4.7.2 EXCEPTIONS TO NEC 250.66 .......................................................................................4-8
4.8 MAIN BONDING JUMPER.........................................................................................................4-9
4.9 SYSTEM WITH GROUNDED CONDUCTOR..........................................................................4-10
Section 5
4.10 EQUIPMENT GROUNDING CONDUCTOR............................................................................4-12
4.10.1 SIZING THE EQUIPMENT GROUNDING CONDUCTOR ............................................4-12
4.10.2 SEPARATE EQUIPMENT GROUNDING CONDUCTORS...........................................4-13
4.11 UNGROUNDED SYSTEMS.....................................................................................................4-13
4.12 GROUNDING A SEPARATELY DERIVED SYSTEM..............................................................4-14
4.13 GROUNDING ELECTRODE SYSTEM....................................................................................4-15
4.14 GROUND-FAULT PROTECTION OF EQUIPMENT ...............................................................4-16
4.15 PERSONNEL PROTECTIVE GROUNDS ...............................................................................4-16
4.15.1 PURPOSE OF PERSONNEL PROTECTIVE GROUNDS.............................................4-16
4.15.2 CRITERIA FOR PERSONNEL PROTECTIVE GROUNDS...........................................4-17
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4.15.3 GROUNDING CLAMPS.................................................................................................4-18
4.15.4 SCREW-TIGHTENING DEVICES .................................................................................4-18
4.15.5 GROUNDING CABLE LENGTH ....................................................................................4-18
4.15.6 GROUNDING CABLE CONNECTION...........................................................................4-18
4.15.7 CONNECTING GROUNDING CABLES IN SEQUENCE ..............................................4-18
4.15.8 REMOVING PROTECTIVE GROUNDS........................................................................4-18
4.15.9 PROTECTIVE APPAREL AND EQUIPMENT ...............................................................4-18
5.0 SPECIAL OCCUPANCIES............................................................................................................5-1
5.1 EXPLOSIVES.............................................................................................................................5-1
5.1.1 EVACUATION..................................................................................................................5-1
5.1.2 SHUTDOWN OF OPERATIONS .....................................................................................5-1
5.1.3 LIGHTNING PROTECTION.............................................................................................5-1
5.1.4 STATIC ELECTRICITY....................................................................................................5-2
5.1.4.1 BONDING AND GROUNDING EQUIPMENT .............................................................5-2
5.1.4.2 TESTING EQUIPMENT GROUNDING SYSTEMS.....................................................5-2
5.1.4.3 CONDUCTIVE FLOORS, SHOES, MATS, AND WRISTBANDS................................5-3
5.1.4.4 SPECIFICATIONS FOR CONDUCTIVE FLOORS AND WRISTBANDS ...................5-3
5.1.4.5 CONDUCTIVE FLOOR TEST .....................................................................................5-3
5.1.4.6 HUMIDIFICATION .......................................................................................................5-4
5.1.4.7 GROUND-FAULT CIRCUIT INTERRUPTER..............................................................5-5
5.1.5 ELECTRICAL EQUIPMENT AND WIRING .....................................................................5-5
Section 6
5.1.5.1 PERMANENT EQUIPMENT AND WIRING.................................................................5-5
5.1.5.2 HAZARDOUS LOCATIONS ........................................................................................5-5
5.1.5.3 ELECTRICAL SUPPLY SYSTEMS .............................................................................5-6
5.1.5.4 BUILDING SERVICE ENTRANCE..............................................................................5-7
5.1.6 TESTING..........................................................................................................................5-7
5.1.6.1 TEST SETUP...............................................................................................................5-8
5.1.6.2 PIN SWITCHES AND OTHER NONINITIATING CIRCUITS ......................................5-8
5.1.6.3 LIGHTNING STORMS.................................................................................................5-8
5.1.6.4 LOW-ENERGY ELECTROEXPLOSIVE DEVICES.....................................................5-8
5.1.6.5 WARNING SIGNALS.................................................................................................5-11
5.1.6.6 FIRING LEADS..........................................................................................................5-11
5.1.6.7 ELECTRICAL TESTING INSTRUMENTS FOR USE WITH EXPLOSIVES
SYSTEMS..................................................................................................................5-11
5.1.6.7.1 CLASSIFICATION.................................................................................................5-11
5.1.6.7.2 CERTIFICATION...................................................................................................5-11
5.1.6.7.3 ELECTRICAL TESTING INSTRUMENTS FOR USE WITH INITIATING
ELECTRICAL CIRCUITS ......................................................................................5-12
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5.1.6.7.4 ELECTRICAL TESTING INSTRUMENTS FOR USE WITH NONINITIATING
ELECTRICAL CIRCUITS ......................................................................................5-12
5.2 PREVENTION OF EXTERNAL IGNITION AND EXPLOSION ................................................5-12
5.2.1 SOURCES OF IGNITION ..............................................................................................5-13
5.2.2 COMBUSTION PRINCIPLES ........................................................................................5-14
5.2.3 EVALUATION OF HAZARDOUS AREAS .....................................................................5-14
5.2.4 INTRINSICALLY SAFE EQUIPMENT ...........................................................................5-14
5.2.5 ENCLOSURES ..............................................................................................................5-14
5.2.6 PURGING/PRESSURIZATION SYSTEMS ...................................................................5-16
5.3 HAZARDOUS LOCATIONS.....................................................................................................5-17
5.3.1 CLASS I .........................................................................................................................5-17
5.3.1.1 DIVISION 1 ................................................................................................................5-17
5.3.1.2 DIVISION 2 ................................................................................................................5-21
Section 7
5.3.2 CLASS II ........................................................................................................................5-21
5.3.2.1 CLASS II DIVISION 1 ................................................................................................5-21
5.3.2.2 CLASS II DIVISION 2 ................................................................................................5-23
5.3.3 GROUPS........................................................................................................................5-23
5.3.4 IGNITION TEMPERATURE...........................................................................................5-23
5.3.5 FLAMMABLE (EXPLOSION) LIMITS ............................................................................5-23
5.3.6 FLASHPOINT.................................................................................................................5-24
5.4 ELECTRICAL EQUIPMENT FOR CLASS I, II, AND III AREAS ..............................................5-24
5.4.1 SEALS AND DRAINS ....................................................................................................5-24
5.4.1.1 SEALS .......................................................................................................................5-24
5.4.1.2 DRAINS .....................................................................................................................5-25
5.4.1.3 SELECTION OF SEALS AND DRAINS ....................................................................5-25
5.4.1.3.1 PRIMARY CONSIDERATIONS.............................................................................5-25
5.4.1.3.2 TYPES OF SEALING FITTINGS...........................................................................5-26
5.5 MANUFACTURERS' DIGEST..................................................................................................5-26
5.6 DESCRIPTIONS, FEATURES, AND TEST CRITERIA OF ENCLOSURES FOR
HAZARDOUS (CLASSIFIED) LOCATIONS (PER NEMA 250)...............................................5-27
5.7 TYPE 7 ENCLOSURES ...........................................................................................................5-27
5.7.1 DESCRIPTION AND APPLICATION.............................................................................5-27
5.7.2 FEATURES AND TEST CRITERIA ...............................................................................5-28
5.8 TYPE 8 ENCLOSURES ...........................................................................................................5-28
5.8.1 DESCRIPTION AND APPLICATION.............................................................................5-28
5.8.2 FEATURES AND TEST CRITERIA ...............................................................................5-28
5.9 TYPE 9 ENCLOSURES ...........................................................................................................5-29
5.9.1 DESCRIPTION AND APPLICATION.............................................................................5-29
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5.9.2 FEATURES AND TEST CRITERIA ...............................................................................5-29
5.10 UNDERGROUND FACILITIES ................................................................................................5-29
5.10.1 WORK ON ELECTRICAL EQUIPMENT AND CIRCUITS.............................................5-30
5.10.2 GROUNDING.................................................................................................................5-31
Section 8
5.10.3 POWER CABLES AND CONDUCTORS.......................................................................5-31
5.10.4 TRAILING CABLES .......................................................................................................5-32
5.10.5 TROLLEY CIRCUITS FOR TRACK HAULAGE ............................................................5-32
6.0 REQUIREMENTS FOR SPECIFIC EQUIPMENT ........................................................................6-1
6.1 CONVEYING SYSTEMS ...........................................................................................................6-1
6.1.1 ELECTRICAL DESIGN CRITERIA ..................................................................................6-1
6.2 CRANES AND HOISTS .............................................................................................................6-2
6.2.1 NEC GENERAL REQUIREMENTS .................................................................................6-2
6.2.2 DISCONNECTING MEANS .............................................................................................6-3
6.2.3 GROUNDING...................................................................................................................6-4
6.2.4 CONTROL........................................................................................................................6-4
6.2.5 CLEARANCES.................................................................................................................6-5
6.2.6 OSHA AND NEC REQUIREMENTS................................................................................6-5
6.2.7 MAINTENANCE AND OPERATIONS..............................................................................6-5
6.2.8 DOCUMENTED MAINTENANCE....................................................................................6-5
6.2.9 MECHANICAL ELEVATING AND ROTATING EQUIPMENT .........................................6-6
6.3 ELEVATORS AND ESCALATORS............................................................................................6-7
6.3.1 CODES AND STANDARDS ............................................................................................6-7
6.3.2 DESIGN SPECIFICATIONS ............................................................................................6-7
6.3.2.1 VOLTAGE AND CURRENT LIMITATIONS.................................................................6-7
6.3.2.2 CONDUCTORS...........................................................................................................6-8
6.3.2.3 DISCONNECTING MEANS.........................................................................................6-8
6.3.2.4 MOTORS .....................................................................................................................6-9
6.3.2.5 GROUNDING ..............................................................................................................6-9
6.3.2.6 OVERSPEED PROTECTION......................................................................................6-9
6.3.3 EMERGENCY POWER ...................................................................................................6-9
6.3.4 DESIGN ...........................................................................................................................6-9
6.3.5 FIRE PROTECTION ......................................................................................................6-10
Section 9
6.3.6 INSPECTIONS AND RECORDS...................................................................................6-11
6.3.6.1 CODES ......................................................................................................................6-11
6.3.6.2 INSPECTOR QUALIFICATIONS...............................................................................6-11
6.4 PORTABLE AND VEHICLE-MOUNTED GENERATORS .......................................................6-11
6.5 BATTERIES .............................................................................................................................6-12
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6.5.1 SURROUNDING SPACE...............................................................................................6-12
6.5.2 LOCATION.....................................................................................................................6-12
6.5.3 VENTILATION................................................................................................................6-12
6.5.4 CONDUIT.......................................................................................................................6-13
6.5.5 BATTERY ROOM ..........................................................................................................6-13
6.5.6 PERSONAL PROTECTIVE EQUIPMENT.....................................................................6-13
6.5.7 TOOLS ...........................................................................................................................6-13
6.5.8 STORAGE BATTERIES AND BATTERY BANKS.........................................................6-14
6.5.8.1 TYPES OF HAZARDS...............................................................................................6-14
6.5.8.2 DESIGN AND CONSTRUCTION CRITERIA ............................................................6-14
6.5.8.3 OPERATING CRITERIA............................................................................................6-15
7.0 WORK IN EXCESS OF 600 VOLTS.............................................................................................7-1
7.1 RESPONSIBILITIES FOR SAFETY...........................................................................................7-1
7.1.1 WORKERS.......................................................................................................................7-1
7.1.2 SUPERVISORS ...............................................................................................................7-2
7.2 TRAINING ..................................................................................................................................7-3
7.2.1 EMPLOYEE TRAINING ...................................................................................................7-3
7.2.2 QUALIFIED EMPLOYEE TRAINING...............................................................................7-3
7.3 JOB BRIEFINGS........................................................................................................................7-3
7.4 PERSONAL PROTECTIVE EQUIPMENT AND PROTECTIVE CLOTHING.............................7-4
7.4.1 SHOES.............................................................................................................................7-4
7.4.2 HARDHATS .....................................................................................................................7-4
Section 10
7.4.3 EYE PROTECTORS........................................................................................................7-5
7.4.5 METAL FASTENERS.......................................................................................................7-5
7.4.6 WORK GLOVES ..............................................................................................................7-5
7.4.7 WORK CLOTHES............................................................................................................7-5
7.4.8 FIRE-RESISTANT (FR) CLOTHING................................................................................7-5
7.4.8.1 GENERAL....................................................................................................................7-5
7.4.8.2 ELECTRIC ARC HAZARDS ........................................................................................7-5
7.4.8.3 TYPES OF FIRE RESISTANT FABRICS....................................................................7-6
7.4.8.4 CLOTHING SYSTEMS................................................................................................7-6
7.4.9 RUBBER GLOVES ..........................................................................................................7-6
7.4.10 RUBBER LINE HOSE, HOODS, COVERS, SLEEVES, AND BLANKETS .....................7-7
7.4.11 LIVE LINE TOOLS ...........................................................................................................7-7
7.4.12 STOREROOM STORAGE...............................................................................................7-7
7.4.13 TRUCK STORAGE ..........................................................................................................7-7
7.4.14 PLACING OF INSULATING GOODS ON CONDUCTORS.............................................7-8
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7.4.15 REMOVING INSULATING GOODS FROM CONDUCTORS..........................................7-8
7.4.16 CLEANING AND INSPECTING.......................................................................................7-8
7.5 PROTECTIVE GROUNDING OF LINES AND EQUIPMENT ....................................................7-8
7.5.1 PURPOSE........................................................................................................................7-8
7.5.1.1 REDUCE THE POTENTIAL VOLTAGE DIFFERENCES ACROSS THE WORKER..7-9
7.5.2 APPLICATION .................................................................................................................7-9
7.5.2.1 DEENERGIZED LINES ...............................................................................................7-9
7.5.2.2 NEW CONSTRUCTION OR DISMANTLING OF FACILITIES..................................7-10
7.5.2.3 MINIMUM APPROACH DISTANCE FROM UNGROUNDED CONDUCTORS........7-10
7.5.2.4 VISIBLE THREE-PHASE SHORT AND GROUND REQUIRED...............................7-10
7.5.2.5 GROUND CIRCUIT ...................................................................................................7-10
7.5.3 GROUNDING EQUIPMENT ..........................................................................................7-11
7.5.3.1 AVAILABILITY ...........................................................................................................7-11
7.5.3.2 APPROVED CAPACITY............................................................................................7-11
7.5.3.3 GROUNDING CABLES AND HARDWARE ..............................................................7-11
Section 11
7.5.3.4 GROUNDING CABLES .............................................................................................7-11
7.5.3.4.1 STRANDING .........................................................................................................7-11
7.5.3.4.2 JACKETS ..............................................................................................................7-11
7.5.3.4.3 FERRULES ...........................................................................................................7-12
7.5.3.4.4 HANDLING OF GROUNDING CABLE .................................................................7-12
7.5.3.4.5 SIZE OF GROUNDING CABLE ............................................................................7-12
7.5.3.4.6 GROUNDING CABLE LENGTH............................................................................7-12
7.5.3.4.7 GROUNDING CLAMPS ........................................................................................7-12
7.5.3.4.7.1 CLAMP TYPES...............................................................................................7-12
7.5.3.4.7.2 CLAMP JAWS.................................................................................................7-13
7.5.3.4.8 GROUNDING CLUSTER BARS ...........................................................................7-13
7.5.3.4.9 TEMPORARY GROUND RODS ...........................................................................7-13
7.5.4 TESTING BEFORE INSTALLING GROUNDS ..............................................................7-14
7.5.5 ATTACHING AND REMOVING GROUNDS .................................................................7-14
7.5.6.1 WORK LOCATION ....................................................................................................7-14
7.5.6.3 OTHER LOCATIONS ................................................................................................7-15
7.5.7 TESTING WITHOUT GROUNDS ..................................................................................7-15
7.5.8 GROUND PERSONNEL................................................................................................7-15
7.6 INSTALLING OR REMOVING CONDUCTORS ......................................................................7-15
7.6.1 WORKING ON ENERGIZED LINE OR EQUIPMENT...................................................7-15
7.6.2 STRINGING OR REMOVING DEENERGIZED CONDUCTORS..................................7-16
7.6.3 STRINGING ADJACENT TO ENERGIZED LINES .......................................................7-17
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7.7 SPECIAL TOOLS.....................................................................................................................7-18
7.7.1 LINEWORKERS’ CLIMBING TOOLS............................................................................7-18
7.7.2 BODY BELTS AND SAFETY STRAPS .........................................................................7-18
7.7.3 TOOL BAG AND EQUIPMENT......................................................................................7-19
7.7.4 TAPES AND RULERS ...................................................................................................7-19
7.7.5 SPOON AND SHOVELS ...............................................................................................7-19
7.7.6 PIKE POLES..................................................................................................................7-20
Section 12
7.7.7 HAND AXES AND SHARP TOOLS...............................................................................7-20
7.7.8 HANDLINES AND TAGLINES .......................................................................................7-20
7.8 TREE TRIMMING.....................................................................................................................7-20
7.8.1 CARE AND USE OF TOOLS.........................................................................................7-20
7.8.2 CLIMBING......................................................................................................................7-20
7.9 SERIES STREET-LIGHTING CIRCUITS AND APPARATUS.................................................7-21
7.10 UNDERGROUND.....................................................................................................................7-21
7.10.1 WORKING IN MANHOLES, UTILITY TUNNELS, AND VAULTS .................................7-21
7.10.2 WORKING ON ENERGIZED UNDERGROUND CABLES............................................7-23
7.10.3 TERMINALS OF UNDERGROUND CABLES (POTHEADS)........................................7-23
7.11 FERRO-RESONANCE.............................................................................................................7-23
8.0 TEMPORARY WIRING.................................................................................................................8-1
8.1 REQUIREMENTS AND INSTALLATION CONDITIONS OF USE.............................................8-1
8.1.1 CONTACT PREVENTION ...............................................................................................8-1
8.1.2 VERTICAL CLEARANCES ..............................................................................................8-1
8.1.3 WET LOCATIONS ...........................................................................................................8-1
8.1.4 SUPPORTS .....................................................................................................................8-1
8.1.5 CONDUIT.........................................................................................................................8-2
8.1.6 LIGHTING ........................................................................................................................8-2
8.1.7 CONFINED SPACES.......................................................................................................8-2
8.1.8 EXPOSED SOCKETS AND BROKEN BULBS................................................................8-2
8.1.9 GROUND FAULT PROTECTION FOR PERSONNEL....................................................8-2
8.1.10 WIRING METHODS.........................................................................................................8-2
8.1.10.1 SERVICE CONDUCTORS ..........................................................................................8-3
8.1.10.2 FEEDER CONDUCTORS ...........................................................................................8-3
8.1.10.3 BRANCH CIRCUIT CONDUCTORS...........................................................................8-3
8.1.10.4 NONMETALLIC SHEATHED CABLE..........................................................................8-3
8.2 USING ASSURED EQUIPMENT GROUNDING CONDUCTOR PROGRAM ...........................8-3
8.3 PORTABLE ELECTRICAL TOOLS AND EQUIPMENT ............................................................8-5
Section 13
8.3.1 INSPECTION AND MAINTENANCE ...............................................................................8-5
DOE-HDBK-1092-2004
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8.3.2 CONDITIONS OF USE ....................................................................................................8-6
8.3.3 USE OF EXTENSION CORDS........................................................................................8-6
8.3.4 DOUBLE INSULATED TOOLS........................................................................................8-6
9.0 ENCLOSED ELECTRICAL/ELECTRONIC EQUIPMENT ............................................................9-1
9.1 PURPOSE..................................................................................................................................9-1
9.2 SCOPE.......................................................................................................................................9-1
9.3 GROUNDING AND BONDING ..................................................................................................9-1
9.3.1 OBJECTIONAL CURRENT OVER GROUNDING CONDUCTORS................................9-1
9.3.2 EQUIPMENT GROUNDING CONDUCTOR....................................................................9-2
9.3.3 ENCLOSURE GROUNDING AND BONDING.................................................................9-3
9.3.4 SPECIAL CONSIDERATIONS ........................................................................................9-5
9.4 RACK POWER DISTRIBUTION ................................................................................................9-6
9.4.1 GENERAL REQUIREMENTS APPLYING TO ALL AC POWER EQUIPMENT
WITHIN OR ATTACHED TO INSTRUMENT RACKS .....................................................9-6
9.4.1.1 LOADS.........................................................................................................................9-6
9.4.1.2 OTHER GENERAL EQUIPMENT REQUIREMENTS .................................................9-6
9.4.2 CONDUCTORS AND CABLES SPECIFIC REQUIREMENTS. ......................................9-6
9.4.2.1 FLEXIBLE CABLES.....................................................................................................9-7
9.4.2.2 STRAIN RELIEF ..........................................................................................................9-7
9.4.2.3 SEPARATION OF VOLTAGES ...................................................................................9-7
9.4.2.4 OTHER CONCERNS...................................................................................................9-8
9.4.3 POWER SWITCHES AND INTERLOCK DEVICES SPECIFIC REQUIREMENTS ........9-8
9.5 CHASSIS POWER DISTRIBUTION ..........................................................................................9-8
9.5.1 AC POWER DISTRIBUTION ...........................................................................................9-8
9.5.1.1 CHASSIS BONDING AND GROUNDING...................................................................9-8
9.5.1.2 CONNECTIONS, CONNECTORS, AND COUPLINGS ..............................................9-9
9.5.1.3 TERMINALS/LIVE PARTS ........................................................................................9-10
9.5.2 DC POWER DISTRIBUTION.........................................................................................9-10
9.6 PROTECTIVE DEVICES FOR ENCLOSED ELECTRICAL/ ELECTRONIC EQUIPMENT.....9-10
Section 14
9.6.1 SURGE ARRESTERS ...................................................................................................9-10
9.6.2 FUSES ...........................................................................................................................9-11
9.6.3 CIRCUIT BREAKERS....................................................................................................9-11
9.6.4 POWER INTERLOCK DEVICES...................................................................................9-11
9.7 DISCONNECTING MEANS .....................................................................................................9-11
9.7.1 GENERAL......................................................................................................................9-12
9.7.2 EMERGENCY SHUTDOWN..........................................................................................9-12
9.7.3 SPECIAL CONSIDERATIONS ......................................................................................9-12
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9.8 MARKING AND LABELING REQUIREMENTS.......................................................................9-13
9.8.1 GENERAL MARKING REQUIREMENTS......................................................................9-13
9.8.2 HAZARD MARKING REQUIREMENTS ........................................................................9-13
9.8.3 OTHER REQUIREMENTS ............................................................................................9-13
9.9 WORKING CLEARANCES ......................................................................................................9-14
9.10 CABLE/UTILITY MANAGEMENT SYSTEM ............................................................................9-15
9.10.1 USAGE WITH ENCLOSED ELECTRICAL/ELECTRONIC EQUIPMENT .....................9-15
9.10.2 REQUIREMENTS ..........................................................................................................9-16
9.11 ELECTRICAL SAFETY REQUIREMENTS FOR TESTER FACILITIES..................................9-17
9.11.1 AMPACITY OF FACILITY WIRING AND DISTRIBUTION EQUIPMENT......................9-17
9.11.2 FACILITY GROUNDING AT TEMPORARY OR REMOTE SITES................................9-17
9.11.3 FACILITY LIGHTNING PROTECTION..........................................................................9-18
9.11.4 SURGE PROTECTION..................................................................................................9-18
9.12 ENCLOSED POWER ELECTRONICS ....................................................................................9-18
9.12.1 ENCLOSURES ..............................................................................................................9-18
9.12.2 COMPONENT CLEARANCES ......................................................................................9-18
9.12.3 INSTRUMENTATION.....................................................................................................9-19
9.12.4 GENERAL......................................................................................................................9-19
9.13 NON-IONIZING RADIATION ...................................................................................................9-20
9.13.1 ELECTROMAGNETIC RADIATION ..............................................................................9-20
9.13.2 ELECTROMAGNETIC RADIATION THREAT TO ELECTROEXPLOSIVE
DEVICES .......................................................................................................................9-20
Section 15
10.0 RESEARCH & DEVELOPMENT ................................................................................................10-1
10.1 PURPOSE................................................................................................................................10-1
10.2 SCOPE.....................................................................................................................................10-1
10.3 COMPLIANCE WITH OSHA....................................................................................................10-1
10.4 STANDARDIZED SAFETY PRACTICES AND PROCEDURES .............................................10-2
10.5 EQUIPMENT NOT LISTED BY A NATIONALLY RECOGNIZED TESTING LABORATORY .10-2
10.5.1 HAZARDS......................................................................................................................10-2
10.5.2 DESIGN AND CONSTRUCTION...................................................................................10-2
10.6 OPERATION AND MAINTENANCE ........................................................................................10-4
10.7 EMPLOYEE QUALIFICATIONS ..............................................................................................10-4
10.7.1 HAZARDS......................................................................................................................10-4
10.7.2 ADDITIONAL QUALIFICATIONS ..................................................................................10-4
10.8 GENERIC R&D EQUIPMENT..................................................................................................10-4
10.8.1 POWER SOURCES.......................................................................................................10-5
10.8.1.1 HAZARDS..................................................................................................................10-5
DOE-HDBK-1092-2004
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10.8.1.2 DESIGN AND CONSTRUCTION ..............................................................................10-5
10.8.1.3 OPERATION AND MAINTENANCE........................................................................10-6
10.8.2 CONDITIONS OF LOW VOLTAGE AND HIGH CURRENT..........................................10-6
10.8.2.1 HAZARDS .................................................................................................................10-6
10.8.2.2 DESIGN AND CONSTRUCTION ...............................................................................10-7
10.8.2.3 OPERATION AND MAINTENANCE........................................................................10-8
10.8.3 CONDITIONS OF HIGH VOLTAGE AND LOW CURRENT..........................................10-8
10.8.3.1 HAZARDS .................................................................................................................10-8
10.8.3.2 DESIGN CONSIDERATIONS ..................................................................................10-8
10.8.3.3 SAFETY PRACTICES................................................................................................10-9
10.8.4 RADIO-FREQUENCY/ MICROWAVE RADIATION AND FIELDS ................................10-9
10.8.4.1 HAZARDS..................................................................................................................10-9
10.8.4.2 DESIGN AND CONSTRUCTION .............................................................................10-10
10.8.4.2.1 EXEMPTIONS FROM RFMW EXPOSURE LIMITS..........................................10-10
Section 16
10.8.4.2.2 EXPOSURE CRITERIA FOR PULSED RFMW RADIATION............................10-11
10.9 METHODS .............................................................................................................................10-13
10.9.1 WIRING METHODS.....................................................................................................10-13
10.9.1.1 HAZARDS ...............................................................................................................10-13
10.9.1.2 DESIGN AND CONSTRUCTION...........................................................................10-14
10.9.1.2.1 DESIGN AND CONSTRUCTION AS AN INTEGRAL PART OF
EQUIPMENT ....................................................................................................10-14
10.9.1.2.2 POWER SUPPLY INTERFACE BETWEEN UTILITY SYSTEMS AND
R&D EQUIPMENT ...........................................................................................10-14
10.9.1.3 OPERATION AND MAINTENANCE......................................................................10-15
10.9.2 UNCONVENTIONAL PRACTICES..............................................................................10-15
10.9.2.1 GROUNDING..........................................................................................................10-15
10.9.2.1.1 HAZARDS ........................................................................................................10-15
10.9.2.1.2 DESIGN AND CONSTRUCTION....................................................................10-15
10.9.2.1.3 NOISE COUPLING MECHANISMS................................................................10-16
10.9.2.1.4 OPERATION AND MAINTENANCE..................................................................10-20
10.9.2.2 MATERIALS USED IN AN UNCONVENTIONAL MANNER.....................................10-21
10.9.2.2.1 HAZARDS ........................................................................................................10-21
10.9.2.2.2 DESIGN AND CONSTRUCTION....................................................................10-22
10.9.2.2.3 OPERATION AND MAINTENANCE ...............................................................10-22
10.9.3 WORK ON ENERGIZED OR DE-ENERGIZED ELECTRICAL EQUIPMENT.............10-23
10.10 REQUIREMENTS FOR SPECIFIC R&D EQUIPMENT....................................................10-23
10.10.1 CAPACITORS..............................................................................................................10-23
10.10.1.1 HAZARDS ...............................................................................................................10-23
DOE-HDBK-1092-2004
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10.10.1.2 DESIGN AND CONSTRUCTION ............................................................................10-24
10.10.1.2.1 AUTOMATIC DISCHARGE DEVICES..........................................................10-24
10.10.1.2.2 SAFETY GROUNDING .................................................................................10-25
10.10.1.2.3 GROUND HOOKS .........................................................................................10-25
10.10.1.2.4 DISCHARGE EQUIPMENT WITH STORED ENERGY IN EXCESS OF
10 JOULES.....................................................................................................10-25
10.10.1.2.5 FUSING ..........................................................................................................10-26
Section 17
10.10.1.3 OPERATION AND MAINTENANCE........................................................................10-26
10.10.2 INDUCTORS................................................................................................................10-27
10.10.2.1 HAZARDS ...............................................................................................................10-27
10.10.2.2 DESIGN AND CONSTRUCTION ............................................................................10-27
10.10.2.3 OPERATION AND MAINTENANCE........................................................................10-28
10.10.3 ELECTRICAL CONDUCTORS AND CONNECTORS.................................................10-28
10.10.3.1 HAZARDS................................................................................................................10-28
10.10.3.2 DESIGN AND CONSTRUCTION ............................................................................10-29
10.10.3.3 OPERATION AND MAINTENANCE........................................................................10-29
10.10.4 INDUCTION AND DIELECTRIC HEATING EQUIPMENT ..........................................10-29
10.10.4.1 HAZARDS................................................................................................................10-29
10.10.4.2 DESIGN AND CONSTRUCTION ............................................................................10-30
10.10.4.3 OPERATION AND MAINTENANCE........................................................................10-30
10.10.5 LASERS AND X-RAY EQUIPMENT............................................................................10-30
10.10.5.1 HAZARDS................................................................................................................10-30
11.0 ELECTRICAL SAFETY DURING EXCAVATIONS.....................................................................11-1
11.1 GENERAL ................................................................................................................................11-1
11.2 REGULATIONS, CODES AND REFERENCES ......................................................................11-1
11.3 UTILITIES IDENTIFICATION...................................................................................................11-2
11.3.1 CONFIGURATION MANAGEMENT..............................................................................11-2
11.3.2. EXCAVATION PERMIT............................................................................................11-2
11.4 UTILITIES VERIFICATION AND MARKING............................................................................11-3
11.4.1 FIELD LOCATION OF EXCAVATION BOUNDARIES ..................................................11-4
11.4.2 LOCATOR EQUIPMENT SELECTION AND LIMITATIONS .........................................11-4
11.4.3 LOCATOR OPERATOR TRAINING ..............................................................................11-6
11.4.4 FIELD MARKING OF IDENTIFIED UTILITIES ..............................................................11-6
11.5 UTILITIES DISPOSITION ........................................................................................................11-7
11.6 WORK CONTROL DURING EXCAVATIONS .........................................................................11-7
11.6.1 SAFETY EQUIPMENT AND PROCEDURES ...............................................................11-7
Section 18
11.7 THE EXCAVATION PROCESS ...............................................................................................11-8
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11.7.1 EXCAVATIONS IN CONCRETE WALLS AND SLABS.................................................11-8
11.7.2 MACHINE OR HAND DIGGING ....................................................................................11-8
11.7.3 WORKER PROTECTION ..............................................................................................11-9
11.8 AS-BUILT DRAWINGS ............................................................................................................11-9
12.0 REFERENCES............................................................................................................................12-1
APPENDIX A DOE MODEL ELECTRICAL SAFETY PROGRAM............................................................ A-1
APPENDIX B ACRONYMS AND DEFINITIONS ...................................................................................... B-1
B.1 ACRONYMS.............................................................................................................................. B-1
B.2 DEFINITIONS............................................................................................................................ B-3
DEFINITIONS APPLICABLE TO 29 CFR 1910 SUBPART S .............................................................. B-3
DEFINITIONS APPLICABLE TO 29 CFR 1910.269........................................................................... B-17
DEFINITIONS APPLICABLE TO 29 CFR 1926 SUBPART K ............................................................ B-22
DEFINITIONS APPLICABLE TO 29 CFR 1926 SUBPART V ............................................................ B-33
DEFINITIONS APPLICABLE TO SECTIONS 1 THROUGH 10 ......................................................... B-37
APPENDIX C WORK MATRICES – EXAMPLES..................................................................................... C-1
APPENDIX D REGULATION MATRICES ................................................................................................ D-1
DOE-HDBK-1092-2004
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1.0 INTRODUCTION
1.1 PURPOSE
The Electrical Safety Handbook presents the Department of Energy (DOE) safety standards for
DOE field offices or facilities involved in the use of electrical energy. It has been prepared to
provide a uniform set of electrical safety guidance and information for DOE installations to effect
a reduction or elimination of risks associated with the use of electrical energy. The objectives of
this handbook are to enhance electrical safety awareness and mitigate electrical hazards to
employees, the public, and the environment.
1.2 SCOPE
This handbook provides general information to enhance understanding of DOE Orders, national
codes, national standards, and local, state, and federal regulations. This handbook shall not
supersede more stringent requirements in those applicable codes, standards, and regulations.
Each entity should reference its contract documents and determine what legal requirements are
to be followed in the area of electrical safety. These requirements may vary from location to
location. In this document, "shall" refers to requirements from regulatory standards such as
Occupational Safety and Health Administration (OSHA) requirements and relevant DOE Orders
that may or may not apply to your specific location. "Should " refers to guidance from consensus
standards such as the National Electrical Code (NFPA 70), National Electrical Safety Code
(NESC, ANSI C2), and Standard for Electrical Safety in the Workplace (NFPA 70E) which may
or may not apply to your specific location (depending upon your contractual requirements). No
section or portion of this document is intended to stand alone. Each section or portion interacts
with others that are appropriate to support referenced material.
Section 19
The design of new facilities shall conform to relevant DOE Orders and should conform to
industry-recognized engineering design standards. Existing facilities should evaluate their
systems and operations in relation to this handbook, applicable DOE Orders, national codes,
national standards, and local, state, and federal regulations to determine if they comply or if a
safety problem exists. If the evaluation determines that a safety risk exists, corrective actions
should be initiated to bring the systems or operations into compliance with current standards. In
the case of a major renovation of an existing facility, the modification shall comply with current
standards.
Existing facilities shall conform to relevant DOE Orders and should comply with the National
Electrical Code (NFPA 70), National Electrical Safety Code (NESC, ANSI C2), and Standard for
Electrical Safety in the Workplace (NFPA 70E). The OSHA standards have specific
requirements that shall apply to all electrical installations and utilization equipment regardless of
when they were designed or installed and identify other mandatory provisions and specify
effective dates. Installations in compliance with the code at the time of design or installation
(code of record), do not need to be upgraded to the updated code unless required to correct a
known hazard or a major modification is being performed unless otherwise directed by OSHA.
This handbook is being provided to identify those DOE Orders, national codes, national
standards, and local, state, and federal regulations that will provide employees with guidance on
requirements pertaining to electrical systems. It is the responsibility of each site to evaluate
compliance with the above requirements.
DOE-HDBK-1092-2004
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1.3 AUTHORITY HAVING JURISDICTION (AHJ)
In states and municipalities, an official (electrical inspector, engineer, or equivalent qualified
individual) is usually designated as the electrical Authority Having Jurisdiction (AHJ). The AHJ
should possess such executive ability as is required for performance of the position, and should
have thorough knowledge of standard materials and work practices used in the installation,
operation, construction, and maintenance of electrical equipment. The AHJ should, through
experience or education, be knowledgeable of the requirements contained in the OSHA
standards, the National Electrical Code, the National Electrical Safety Code, DOE requirements,
and other appropriate local, state, and national standards. The AHJ should be responsible to
interpret codes, regulations and standards, and approve equipment, assemblies, or materials. If
the AHJ needs to address items outside his or her electrical expertise, such as fire, confined
space, fall protection, or like issues, the AHJ should consult with cognizant experts before a
decision is reached. The AHJ may permit alternate methods where it is assured that equivalent
objectives can be achieved by establishing and maintaining effective safety equal to or
exceeding established codes, regulations, and standards.
In DOE, levels of authority exist that serve the function of the AHJ. The AHJ may be the
contracting officer, such as an area manager. This person may choose to delegate authority to
an individual or organization within his or her control. It is acceptable for DOE sites to delegate
authority to a committee of subject matter experts. The authority may reside with a safety or
facilities department. The field office manager or designated representative may act as a higher
level of authority. The authority may begin with an electrician and proceed through various
levels of supervision to management (as shown in Fig. 1-1).
Section 20
Fig. 1-1.
NOTE: The titles in Fig. 1-1 will vary from site to site.
DOE-HDBK-1092-2004
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DOE contractors should establish lines of authority within their organizations. It is important that
a line of authority be established, documented, and recognized. The limits of the authority and
recognition of higher authority should be delineated.
DOE-HDBK-1092-2004
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2.0 GENERAL REQUIREMENTS
This section deals with the reliability and effective maintenance of electrical systems that can be
achieved in part by careful planning and proper design. The training of personnel in safety-
related work practices that pertain to their respective job assignments is outlined.
2.1 ELECTRICAL MAINTENANCE OR REPAIRS
Only qualified persons shall perform electrical repairs. Once a problem is discovered while
troubleshooting or maintaining electrical equipment, any further work on this component or
system must be suspended until the associated corrective actions are processed through a
work control system. It is dangerous for an unqualified worker to attempt electrical repair.
Before any electrical maintenance or troubleshooting is performed, sources of electrical energy
shall be deenergized, except where it is necessary for troubleshooting, testing, or areas that are
infeasible to deenergize. All energy sources shall be brought to a safe state. For example,
capacitors shall be discharged and high capacitance elements shall be short-circuited and
grounded.
2.1.1 WORK ON ENERGIZED/DEENERGIZED ELECTRICAL EQUIPMENT
The first consideration for working on any electrical system is to have the circuit positively
deenergized. All circuits and equipment must be considered energized until opened, tagged,
and/or locked according to an approved procedure and should be proven deenergized by
testing with an approved testing device known to be in proper working order. NFPA 70E refers
to this as an electrically safe work condition and defines it as “a state in which the conductor or
circuit part to be worked on or near has been disconnected from energized parts, locked/tagged
in accordance with established standards, tested to ensure the absence of voltage, and
grounded if determined necessary.” The electrical hazard controls identified in NFPA 70E are
intended to protect a person from arc flash and shock hazards. Due to the explosive effects of
some arc events, physical trauma injuries could occur. The personal protective equipment
(PPE) requirement identified in NFPA 70E is intended to protect against physical trauma other
than exposure to the thermal effects of an arc flash.
2.1.2 CONSIDERATIONS FOR WORKING ON ENERGIZED SYSTEMS AND
EQUIPMENT
Qualified employees performing such tasks as electrical repairs, modifications, and tests on
energized electrical systems, parts, and equipment need to comply with the following:
1. Parts to which an employee might be exposed shall be put into an electrically safe work
condition before the employee works on or near them, unless the employer can
demonstrate that deenergizing introduces additional or increased hazards or is infeasible
due to equipment design or operational limitations.
2. Personnel shall not work on energized circuits unless they are qualified to do so, or, for
training purposes, unless they work under the direct supervision of a qualified person.
3. Sufficient protection in the form of insulated tools and insulated protective equipment,
such as gloves, blankets, sleeves, mats, etc., shall be used while working on energized
circuits. (See NFPA 70E)
Section 21
DOE-HDBK-1092-2004
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4. Other work, independent of voltage, that presents a significant shock, arc flash, or arc
blast hazard to employees.
Note: The discussion in #4 above assumes the system voltage is less than the maximum use
voltage of the ASTM class of rubber goods used.
2.1.3. SAFETY WATCH RESPONSIBILITIES AND QUALIFICATIONS
The responsibilities and qualifications of personnel for sites that require the use of a safety
watch are as follows:
1. Trained in cardiopulmonary resuscitation (CPR);
2. Possessing a thorough knowledge of the locations of emergency-shutdown push buttons
and power disconnects in their operations;
3. Possessing a thorough knowledge of the specific working procedures to be followed and
the work to be done;
4. Specific responsibilities include monitoring the work area for unsafe conditions or work
practices and taking necessary action to ensure abatement of the unsafe condition or
work practice, deenergizing equipment and alerting emergency-rescue personnel as
conditions warrant, maintaining visual and audible contact with personnel performing the
work, and removal of injured personnel, if possible; and
5. The safety watch should have no other duties that preclude observing and rendering aid
if necessary.
2.2 BASIC SAFEGUARDS
To protect employees from some of the electrical hazards at industrial sites, Federal regulations
limit the performance of electrical work to qualified and competent personnel. Specifically, the
law requires that only a qualified person or someone working under the direct supervision of a
qualified person may perform any repair, installation, or testing of electrical equipment. See
Section 2.8 and the definitions of "Qualified Employee" or "Qualified Person" in Appendix B.
One of the best ways to prevent electrical accidents at industrial sites is to be aware of electrical
dangers in the workplace. Once hazards have been identified, they must be pointed out and
proper steps taken by a qualified person.
The following, where used, will improve the safety of the workplace:
1. Maintain good housekeeping and cleanliness.
2. Identify and control potential hazards.
3. Anticipate problems.
4. Resist pressure to "hurry up."
5. Plan and analyze for safety in each step of a project.
DOE-HDBK-1092-2004
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6. Document work.
7. Use properly rated test equipment and verify its condition and operation before and after
use.
8. Know and practice applicable emergency procedures.
9. Become qualified in CPR and first aid and maintain current certifications.
10. Wear appropriate PPE.
11. Refer to system drawings and perform system walkdowns.
12. Electrical equipment should be maintained in accordance with the manufacturer’s
instructions.
13. Ensure that work is adequately planned through an approved work control process.
2.3 RESPONSIBILITIES
Management is responsible to provide a workplace that is free from recognized hazards that
might cause injury, illness, or death and to comply with the specific safety and health standards
issued by Federal, state, and local authorities, particularly OSHA. Managers expect their
employees to comply with these regulations as well as the DOE requirements formulated for the
health and safety of employees. Prevention of injury and illness requires the efforts of all and is
a goal well worth achieving.
2.3.1 MANAGEMENT RESPONSIBILITIES
To ensure safety and protection of employees, managers have the following responsibilities:
Section 22
1. Ensure that employees are provided a workplace that is free from recognized hazards.
2. Ensure that employees performing electrical work are trained and qualified (see Section
2.8).
3. Ensure that approved, maintained, and tested personal protective equipment and clothing is
provided, available, and used properly.
4. Establish, implement, and maintain procedures and practices that will ensure safe conduct
of electrical work.
5. Keep and maintain records as required.
2.3.2 EMPLOYEE RESPONSIBILITIES
Employees are responsible to comply with occupational safety and health regulations and
standards that apply to their own actions and conduct, including immediate reporting to
management of unsafe and unhealthful conditions.
DOE-HDBK-1092-2004
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2.4 REVIEWS/INSPECTIONS
All modifications to existing and new facilities and projects should be subject to inspection by
the AHJ or authorized designee to verify compliance with the codes and standards in effect on
the date that the work was approved by a final design review. If the installation involves a
hazard to life, equipment, or property, current standards and codes should be used to mitigate
the hazard.
According to OSHA, all major replacements, modifications, repairs, or rehabilitation performed
after March 15, 1972, on electrical systems and equipment installed before March 15,1972, are
required to comply with all the requirements of 29 CFR 1910.302 to 1910.308. OSHA considers
major replacements, modifications, or rehabilitation to be work similar to that involved when a
new building or facility is built, a new addition is built, or an entire floor is renovated.
2.5 APPROVAL OF ELECTRICAL EQUIPMENT
All electrical equipment, components, and conductors shall be approved for their intended uses.
If any electrical system component is of a kind that any Nationally Recognized Testing
Laboratory (NRTL) accepts, certifies, lists, or labels, then only NRTL accepted, certified, listed,
or labeled components can be used. A nonlisted, nonlabeled, noncertified component may be
used if it is of a kind that no NRTL covers, and then it shall be tested or inspected by the local
authority responsible for enforcing the Code. For example, this would apply to custom-made
equipment. The custom-made equipment should be built in accordance with a design approved
by the AHJ.
See 29 CFR 1910.399 for definitions relating to OSHA requirements for accepting electrical
equipment and wiring methods that are not approved by an NRTL.
2.6 CODES, STANDARDS, AND REGULATIONS
Workers who perform electrical or electronic work, where applicable, shall comply with relevant
DOE Orders that may identify the following codes and standards.
1. Standards published by the National Fire Protection Association (NFPA)
2. National Electrical Safety Code, ANSI C2.
3. All relevant state and local requirements.
4. Components or installations in aircraft, watercraft, and railroads are exempt from the
above approval requirements.
The standards and performance specifications from the following organizations are
recommended and should be observed when applicable:
1. Institute of Electrical and Electronics Engineers (IEEE)
2. National Electrical Manufacturers Association (NEMA)
3. American National Standards Institute (ANSI)
DOE-HDBK-1092-2004
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4. American Society for Testing and Materials (ASTM)
5. National Fire Protection Association (NFPA)
6. Underwriters Laboratory, Inc. (UL)
7. Factory Mutual Engineering Corporation (FMEC)
Section 23
8. Other NRTLs recognized by OSHA on a limited basis.
Where no clear applicable code or standard provides adequate guidance or when questions
regarding workmanship, judgment, or conflicting criteria arise, personnel safety protection shall
be the primary consideration. Therefore, where there are conflicts between the mandatory
requirements of the above codes, standards, and regulations, the requirements that address the
particular hazard and provide the greater safety shall govern.
2.7 GROUND FAULT CIRCUIT INTERRUPTERS (GFCIs) AND ARC
FAULT CIRCUIT INTERRUPTERS (AFCIs)
There are two classes of GFCIs, each with a distinct function. A Class A GFCI trips when the
current to ground has a value in the range of 4 through 6 milliamperes and is used for personnel
protection. A Class A GFCI is suitable for use in branch circuits. A Class B GFCI (commonly
used as ground fault protection for equipment) trips when the current to ground exceeds 20
milliamperes. A Class B GFCI is not suitable for employee protection.
Ground-fault circuit protection can be used in any location, circuit, or occupancy to provide
additional protection from line-to-ground shock hazards because of the use of electric hand
tools. There are four types of GFCIs used in the industry:
1. Circuit breaker type
2. Receptacle type
3. Portable type
4. Permanently mounted type
The condition of use determines the type of GFCI selected. For example, if an electrician or
maintenance person plugs an extension cord into a nonprotected GFCI receptacle, the easiest
way to provide GFCI protection is to utilize a portable-type GFCI.
2.7.1 HOW A GFCI WORKS
See Section 4.14 for ground-fault protection of equipment. GFCIs are devices that sense when
current—even a small amount—passes to ground through any path other than the proper
conductor. When this condition exists, the GFCI quickly opens the circuit, stopping all current
flow to the circuit and to a person receiving the ground-fault shock.
Figure 2-1 shows a typical circuit arrangement of a GFCI designed to protect personnel. The
incoming two-wire circuit is connected to a two-pole, shunt-trip overload circuit breaker. The
load-side conductors pass through a differential coil onto the outgoing circuit. As long as the
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current in both load wires is within specified tolerances, the circuit functions normally. If one of
the conductors comes in contact with a grounded condition or passes through a person's body
to ground, an unbalanced current is established. This unbalanced current is picked up by the
differential transformer, and a current is established through the sensing circuit to energize the
shunt trip of the overload circuit breaker and quickly open the main circuit. A fuse or circuit
breaker cannot provide this kind of protection. The fuse or circuit breaker will trip or open the
circuit only if a line-to-line or line-to-ground fault occurs that is greater than the circuit protection
device rating.
Differential transformers continuously monitor circuits to ensure that all current that flows out to
motor or appliances returns to the source via the circuit conductors. If any current leaks to a
fault, the sensing circuit opens the circuit breaker and stops all current flow.
A GFCI will not protect the user from line-to-line or line-to-neutral contact hazards. For example, if
an employee using a double-insulated drill with a metal chuck and drill bit protected by a GFCI
device drills into an energized conductor and contacts the metal chuck or drill bit, the GFCI device
will not trip (unless it is the circuit the GFCI device is connected to) as it will not detect a current
imbalance.
Section 24
2.7.2 USES
The use of GFCIs in branch circuits for other than dwelling units is defined in the NEC 410.4.
Figure 2-1. GFCI-protected circuits are one way of providing protection of personnel
using electric hand tools on construction sites or other locations.
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Ground-fault protection for personnel shall be provided for temporary wiring installations utilized to
supply temporary power to equipment used by personnel during construction, remodeling,
maintenance, repair, or demolition activities.
For temporary wiring installations;
a) All 120-V, single-phase, 15-, 20-, and 30-A receptacle outlets that are or are not a part of
the permanent wiring of the building or structure and that are in use by employees shall
have GFCI protection for personnel.
b) GFCI protection or an assured equipment grounding program (See Section 8.2) for all other
receptacles shall be used to protect against electrical shocks and hazards.
Portable GFCIs shall be trip-tested according to the manufacturer’s instructions.
2.7.3 ARC FAULT CIRCUIT INTERRUPTERS (AFCIs)
One of the more promising techniques for improvement of performance of wiring systems with
respect to arc-generated fires and intermittent equipment operation is the possibility of using the
arc voltage and current signatures to trip circuits by an AFCI. An AFCI is a device intended to
provide protection from the effects of arc faults by recognizing characteristics unique to arcing
Figure 2-2. There are three methods of providing GFCI protection for construction sites.
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and by functioning to de-energize the circuit when an arc fault is detected (NEC 210.12 and
550.25). AFCIs are evaluated to UL1699, Safety Standard for Arc-Fault Circuit Interrupters,
using testing methods that create or simulate arcing conditions to determine the product’s ability
to detect and interrupt arcing faults.
Although NEC 210.12 requires that AFCI protection be provided on branch circuits that supply
outlets (receptacle, lighting, etc.) in dwelling unit bedrooms, there is no prohibition against
providing AFCI protection on other circuits or location other than the bedrooms. For example,
aircraft wire systems utilize AFCIs for newer installation to trip the circuit routed through
sensitive areas such as fuel storage areas.
2.8 TRAINING AND QUALIFICATIONS OF QUALIFIED WORKERS
Only qualified workers shall perform work on electrical systems. It is dangerous for unqualified
personnel to attempt to do electrical work. There should be an employee training program
implemented to qualify workers in the safety-related work practices that pertain to their
respective job assignments.
2.8.1 FORMAL TRAINING AND QUALIFICATIONS
Management should establish formal training and qualifications for qualified workers before they
are permitted to perform electrical work. Refresher training is recommended at intervals not to
exceed three years to provide an update on new regulations and electrical safety criteria.
The training shall be on-the-job and/or classroom type. The degree of training provided shall be
determined by the risk to the employee. This training shall be documented. Qualified
employees shall be trained and familiar with, but not be limited to, the following:
1. Safety-related work practices, including proper selection and use of PPE, that pertain to
their respective job assignments.
2. Skills and techniques necessary to distinguish exposed live parts from other parts of
electrical equipment.
Section 25
3. Skills and techniques necessary to determine the nominal voltage of exposed live parts,
clearance distances, and the corresponding voltages to which the qualified person will be
exposed.
4. Procedures on how to perform their jobs safely and properly.
5. How to lockout/tagout energized electrical circuits and equipment safely.
Other types of training recommended for electrical workers include the following:
a. National Electrical Code (NFPA 70) (2002)
b. National Electrical Safety Code (ANSI C2) (2002)
c. Use of personal protective grounds
d. Use of testing and measuring equipment
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e. Work permit and work authorization procedures
f. Use and care of personal protective equipment
g. Proper clothing required for arc flash or arc blast protection
h. First-aid and CPR refresher training is recommended at intervals not to exceed 3 years
i. Standard for Electrical Safety in the Workplace (NFPA 70E) (2004)
29 CFR 1910.269(a) and 1910.332 also require training for persons other than qualified workers
if their job assignments bring them close enough to exposed parts of electrical circuits
operating at 50 V or more to ground for a hazard to exist.
2.8.2 TRAINING OF SAFETY PERSONNEL
Safety personnel designated to support electrical safety programs should be knowledgeable
and trained at levels commensurate with their duties.
2.9 WORKING SPACE AROUND ELECTRICAL EQUIPMENT
Working space around electrical enclosures or equipment shall be adequate for conducting all
anticipated maintenance and operations safely, including sufficient space to ensure safety of
personnel working during emergency conditions and workers rescuing injured personnel.
Spacing shall provide the dimensional clearance (discussed in the following subsections) for
personnel access to equipment likely to require examination, adjustment, servicing, or
maintenance while energized. Such equipment include panel boards, switches, circuit breakers,
switchgear, controllers, and controls on heating and air conditioning equipment.
These clearances shall be in accordance with NESC and NEC. These working clearances are
not required if the equipment is not likely to require examination, adjustment, servicing, or
maintenance while energized. However, sufficient access and working space is still required.
2.9.1 ELECTRICAL EQUIPMENT RATED AT 600 VOLTS OR LESS
NEC 110.26 states that a minimum working space 30 in. wide shall be provided in front of
electrical equipment rated at 600 V or less. This provides room to avoid body contact with
grounded parts while working with energized components of the equipment. The 30-in.-wide
space may be centered in front of the equipment or can be offset. The depth of the working
space shall be clear to the floor. Where rear access is required to work on deenergized parts, a
minimum of 30 inches shall be provided. There shall be clearance in the work area to allow at
least a 90-degree opening of equipment doors or hinged panels on the service equipment.
Working spaces may overlap. The depth of the working space shall be 3 ft, 3 1/2 ft, or 4 ft,
depending upon existing conditions. The conditions are as follows:
Condition 1: These are exposed live components on one side of a space and ungrounded parts
on the other side.
Condition 2: The electrical equipment is mounted or set on one wall, and the wall on the
opposite side is grounded. If the qualified worker should accidentally contact the conductive wall
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Section 26
2-10
while touching live components, a circuit would be completed to ground and a fatal shock might
occur.
Condition 3: The electrical equipment is mounted or set on one wall, and additional electrical
equipment is mounted or set on the opposite side of the room. There are live components on
both sides of the room. The qualified worker might accidentally make contact with live
components and be in series with a hot phase and the grounded metal of the electrical
equipment, which could produce a fatal shock.
See Figure 2-3 for the clearance requirements in front of electrical equipment rated 600 V or
less.
Figure 2-3. Minimum clearances in front of electrical equipment (600 V or less).
NEC Table 110.26(A)(1)
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2.9.2 ELECTRICAL EQUIPMENT RATED OVER 600 VOLTS
NEC 110.34 lists minimum clearances required for working spaces in front of high-voltage
electrical equipment such as switchboards, control panels, switches, circuit breakers,
switchgear, and motor controllers.
There are three conditions to apply:
1. Where there are exposed live components on one side of a space and no live or
ungrounded parts on the other side.
2. Where there are exposed live components on one side and grounded parts on the other
such as concrete, brick, and tile walls that are considered to be grounded parts.
3. Where there are exposed live components on both sides.
See Figure 2-4 for the clearance requirements in front of electrical equipment rated at over 600
V. See NEC for clearance requirements in the rear of electrical equipment.
NEC Table 110.34(A)
Figure 2-4. Minimum clearances in front of electrical equipment (over 600 V).
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2.10 IDENTIFICATION OF DISCONNECTION MEANS
Switches in service panels, subpanels, or elsewhere shall be marked to show what loads or
equipment are supplied.
2.10.1 DISCONNECTING MEANS
In according to NEC 110.22, all disconnecting means (disconnect switches or circuit breakers)
shall be located for easy access and shall be clearly and permanently marked to show the
purposes of the disconnects, unless located and arranged so that the purpose is evident.
Labeling should match and be traceable to appropriate drawings. This applies to all existing
electrical systems and all new, modernized, expanded, or altered electrical systems.
Disconnecting means shall be capable of being locked out where required.
2.10.2 PANELBOARD CIRCUIT DIRECTORIES
Panelboard circuit directories shall be provided and fully and clearly filled out.
2.10.3 ENCLOSURE LABELING
Printed labeling or embossed identification plates affixed to enclosures shall comply with the
requirements that disconnects be legibly marked and that the marking shall be of sufficient
durability for the environment involved.
2.10.4 LOAD LABELING
As with the disconnecting device, the load should be labeled. For example, the motor, the
controller, and the disconnecting device could have the same identification number.
2.10.5 SOURCE LABELING
The source supplying power to the disconnecting means and load should be labeled as well.
This requirement allows the electrical worker to know the identification of the elements from the
source of power through the entire circuit. (See Figure 2-5.)
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2.11 WORK INSTRUCTIONS
Before work begins, the qualified worker should ensure that the job to be done is in compliance
with instructions pertaining to the electrical work.
2.11.1 SAFE WORK INSTRUCTIONS AND SUPERVISION
Section 27
Electrical work should be performed according to written safety procedures and approved
electrical safety manuals. Electrical work should be directed by a supervisor who is qualified by
training and experience in the applicable safety-related work practices.
Workers should report any electrical hazards to their immediate supervisor. The supervisor
should take all corrective actions necessary to address an employee's concerns.
Electrical instructions should be based on a thorough analysis of the job and its hazards. If the
same task is repeated, it may be performed under specific work rules that are based on such
analyses.
NEC 110.22
NEC 230.70(B)
NEC 408
Figure 2-5. Switchgear, panel boards, motor control centers, etc., should identify the
loads and elements which they supply.
• NEC section 430.102
• NEC section 430.83
• NEC section 430.7
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2.11.2 WORK INSTRUCTIONS
If no specific instruction is available and the job is beyond the scope of written work rules, the
supervisor should issue instructions pertaining to the job to be performed. The instructions
should contain the essential safety rules for the job and, when documented, should be signed
by the employee, a line supervisor, or safety representative.
2.11.3 WORK PLANNING
Electrical instructions may include, but not be limited to, the following:
1. Deenergizing circuits, if possible, and providing a means to prevent reenergization
(lockout/tagout)
2. Grounding conductors and all possible conducting parts
3. Controlling associated generating equipment
4. Testing of equipment to ensure safe conditions
5. Provision of rubber-insulated protective equipment rated for the highest voltage present
6. Qualified personnel (see 2.1.2 and 2.1.3)
7. PPE and protective clothing (e.g., hardhats, safety shoes, eye and face protection,
insulated live-line tools, hot sticks, cotton or fire-resistant clothing, and arc protection)
8. Working on experimental equipment
2.12 ELECTRICAL PERSONAL PROTECTIVE EQUIPMENT
Qualified workers are responsible for avoiding and preventing accidents while performing
electrical work, repairs, or troubleshooting electrical equipment. Personnel shall wear or use
PPE and protective clothing that is appropriate for safe performance of work. Qualified workers
need to use appropriate arc-fault PPE whenever they work near electrical equipment that could
create an arc flash hazard.
2.12.1 MANAGEMENT'S RESPONSIBILITIES
Managers shall ensure that appropriate PPE is provided and ensure that employees using PPE
are trained in their proper use. Furthermore, managers shall ensure that employees use the
appropriate PPE for their assigned task.
2.12.2 INSPECTING PPE
Employees shall visually inspect rubber-insulated PPE at the beginning of each workday prior to
use and after any work performed that could damage the equipment. Such inspections shall
include a field air test of the gloves used. Visual inspection shall be performed on hot sticks,
grounds, aerial lift equipment and booms, rope, ladders, insulated tools, etc. Equipment that
does not successfully pass visual inspection shall not be used and shall be returned for repair
and testing or disposal.
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2.12.3 CLEANING AND ELECTRICAL TESTING OF PPE
Section 28
Rubber-insulated PPE issued for use shall receive periodic cleaning and electrical testing in
accordance with the requirements of the appropriate ANSI/ASTM standards listed in the
References section of this handbook. The intervals of retest for rubber goods issued for service
shall not be more than 6 months for gloves and 12 months for sleeves and blankets. Gloves or
sleeves that have been electrically tested but not issued for service shall not be placed into
service unless they have been electrically tested within the previous 12 months.
2.12.3.1 TESTING
All testing methods, apparatus, and facilities shall meet the applicable ANSI/ASTM Standard.
The method used and the results of such tests shall be documented and made available for
inspection.
2.12.3.2 TESTING APPARATUS
Testing apparatus shall be operated and maintained by personnel trained for such work.
Calibration schedules and procedures for calibrating testing apparatus are recommended to be
in accordance with ANSI C39.1.
2.12.3.3 RETESTED PPE
Retested rubber-insulated PPE shall be identified to indicate the date of the latest test or date of
retest in accordance with the appropriate standard. Manufacturer's recommendations shall be
followed on the type of paint or ink to be used.
2.12.4 LIVE-LINE TOOLS
Live-line tools shall be cleaned and inspected before use and receive a dielectric test whenever
their insulating value is suspect. A record of the testing of live-line tools shall be maintained.
2.12.4.1 FIBERGLASS-HANDLED TOOLS
Fiberglass-handled tools shall be tested by the manufacturer at 100 kV per ft of length. The in-
service test shall be 75 kV per ft.
2.12.4.2 WOODEN-HANDLED TOOLS
Wooden-handled tools shall be tested by the manufacturer to 75 kV per ft of length. The in-
service test shall be 50 kV per ft.
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2.12.5 MAXIMUM USAGE VOLTAGE
Maximum usage voltage phase-to-phase or phase-to-ground for insulating blankets, mats,
covers, line hose, sleeves, and gloves shall be as follows:
Class Voltage Label Color
00 500 Beige
0 1,000 Red
1 7,500 White
2 17,500 Yellow
3 26,500 Green
4 36,000 Orange
2.12.6 MAXIMUM USAGE VOLTAGE FOR LIVE-LINE TOOLS
Maximum usage voltage per foot of length and phase-to-phase or phase-to-ground for live-line
tools shall be as follows:
1. Tools with wooden handles 69 kV
2. Tools with fiberglass handles 93 kV
2.12.7 RUBBER-INSULATED GLOVES
Whenever rubber-insulated protective gloves are required, approved protective gloves shall also
be worn (See Appendix C) for those conditions where rubber-insulated protective gloves can be
used without protectors.
2.12.8 STORAGE
Electrical insulating and protective clothing and equipment should be stored lying flat,
undistorted, right-side out, and unfolded, as appropriate, in protective containers. Blankets may
be stored rolled provided the inner diameter of the roll is at least 2 in.
Rubber goods shall be stored in a location as cool, dark, and dry as possible. The location shall
be as free as practicable from ozone, chemicals, oils, solvents, damaging vapors and fumes,
and away from electrical discharges and sunlight. Rubber gloves should be stored cuff-down in
a bag, box, or container designed for rubber glove storage. Rubber gloves may be kept inside of
leather protectors.
2.12.9 SAFETY SHOES, HARDHATS, AND GLASSES
Safety shoes, hardhats, and safety glasses worn by electrical workers shall meet the
requirements of ANSI Z41, ANSI Z89.1, and ANSI Z87.1 specifications, respectively.
Section 29
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2.13 WORK PRACTICES
NFPA 70E covers electrical safety-related work practices and procedures for qualified and
unqualified employees who work on or near exposed energized electrical conductors or circuit
parts in workplaces. This information provides a foundation for establishing an electrically safe
working environment. NFPA 70E has embedded four basic strategies in the document. These
strategies are:
1. establish an electrically safe work condition,
2. training,
3. planning the work, and
4. personal protective equipment.
NFPA 70E is updated on a 3-year cycle in compliance with ANSI requirements. This schedule
allows for the latest acceptable technology and experience to be integrated into the document.
2.13.1 TRAINING
Qualified workers shall be knowledgeable and trained in safety-related work practices, safety
procedures, and other requirements that pertain to their respective job assignments. Employees
shall not be permitted to work in an area where they are likely to encounter an electrical hazard
unless they have been trained to recognize and avoid these hazards. (See Section 2.8.)
2.13.1.1 LIVE PARTS
Live parts to which an employee may be exposed shall be deenergized before the employee
works on or near them, unless it can be demonstrated that deenergizing introduces additional or
increased hazards or is infeasible because of equipment design or operational limitations. (See
Section 2.1.1.)
Live parts that operate at less than 50 volts to ground need not be deenergized if there will be
no increased exposure to electrical burns or to explosion due to electrical arcs.
2.13.1.2 SAFE PROCEDURE
Safe procedures for deenergizing circuits and equipment shall be determined before circuits or
equipment are deenergized. Deenergization procedures shall be included in the lockout/tagout
procedure for the circuit or equipment to be deenergized.
2.13.1.3 CIRCUITS AND EQUIPMENT
Circuits and equipment to be worked on shall be disconnected from all electric energy sources.
Control circuit devices such as push-buttons, selector switches, and interlocks shall not be used
as the sole means for deenergizing circuits or equipment.
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2.13.1.4 STORED ELECTRICAL ENERGY
Stored electrical energy that might endanger personnel shall be placed in a safe state.
Capacitors shall be discharged and high-capacitance elements shall be short-circuited and
grounded if the stored electrical energy could endanger personnel.
2.13.1.5 STORED NONELECTRICAL ENERGY
Stored nonelectrical energy in devices that could reenergize electric circuit parts shall be
blocked or relieved to the extent that the circuit parts could not be accidentally energized by the
device. Examples include wound springs and pneumatic-driven devices.
2.13.1.6 LOCKOUT/TAGOUT PROCEDURE
Each employer shall document and implement lockout/tagout procedures to safeguard
employees from injury while they are working on or near deenergized electric circuits and
equipment. The lockout/tagout procedures shall meet the requirement of NFPA 70E 120.2, 29
CFR 1910.147(c) to (f), 1910.269(d) and (m), 1910.333, and 1926.417. (See Figure 2-6.)
2.13.2 VERIFICATION OF DEENERGIZED CONDITION
Verification shall be made that all live circuits, parts, and other sources of electrical energy,
including mechanical energy, have been disconnected, released, or restrained.
Section 30
A qualified worker shall operate the equipment operating controls, perform voltage verification,
and inspect open switches and draw out breakers to ensure that energy sources are isolated.
2.13.2.1 VOLTAGE VERIFICATION TEST
A qualified worker shall use appropriate test equipment to test the circuit elements and electrical
parts of equipment to which employees will be exposed and shall verify that the circuit elements
and equipment parts are deenergized. The test shall also determine if a hazardous energized
condition exists as a result of induced voltage or voltage back feed after specific parts of the
Figure 2-6. Employers shall implement and document a lockout-tagout program with
procedures to safeguard employees from injury while working on or near deenergized
systems.
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circuit have been deenergized. If the circuit to be tested is over 600 V nominal, the test equipment
shall be checked for proper operation immediately before and immediately after this test. This test
is also recommended for systems of 600 V or less. Testing shall be performed as if the circuit is
energized. The voltage verification device used shall be rated for the application. Proximity testers
and solenoid-type devices should not be used to test for the absence of alternating current (AC)
voltage. See 2.13.4.6 for further information.
2.13.2.2 APPLICATION OF GROUNDS
Personnel protective grounds shall be applied on circuits 600 V and above or on lesser voltages
where residual charges may accumulate. Personal protective grounds shall be selected and
installed in accordance with appropriate standards. (See sections 4.6 and 7.5). Consideration
shall be given to step and touch potentials in the area of the temporary ground connections.
2.13.3 REENERGIZING EQUIPMENT
The following requirements shall be met before circuits or equipment are reenergized, even
temporarily.
2.13.3.1 TESTS AND VISUAL INSPECTIONS
A qualified worker shall conduct tests and visual inspections to verify that all personnel are in the
clear and that all tools, electrical jumpers, shorts, grounds, and other such devices have been
removed so that the circuits and equipment can be safely energized.
2.13.3.2 WARNING EMPLOYEES
Employees exposed to the hazards associated with reenergizing the circuit or equipment shall
be warned to stay clear of circuits and equipment.
2.13.3.3 REMOVING LOCK AND TAG
Each lock and tag shall be removed by applying the following:
1. Each lockout or tagout device shall be removed from each energy-isolating device by the
authorized employee who applied the lockout or tagout device, or under their direct
supervision, or as stated below.
2. Exception: When the authorized employee who applied the lockout or tagout device is not
available to remove it, that device may be removed under the direction of his or her
supervisor. Extreme care shall be taken and specific procedures shall be followed, including,
at a minimum, the following elements:
a. Verification by the supervisor that the authorized employee who applied the device is not
at the affected facility
b. Making all reasonable efforts to contact the authorized employee to inform him or her
that the lockout or tagout device has been removed
c. Ensuring that the authorized employee has this knowledge before he or she resumes
work at the affected facility
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2.13.4 SAFE ENERGIZED WORK (HOT WORK)
Section 31
Safety-related work practices shall be used to prevent electrical shock or other electrically
induced injuries when employees work on or near electrical conductors or circuit parts that are
energized. Only qualified workers who are knowledgeable and have been trained to work safely
on energized circuits and to use the appropriate PPE, protective clothing, insulating shielding
materials, and insulated tools shall be permitted to work on energized conductors or circuit
parts.
2.13.4.1 APPROACH DISTANCE
No unqualified employee shall be permitted to approach or take any conductive object closer to
exposed, energized lines or parts than the distance listed in NFPA 70E 130.26, Approach
Boundaries to Live Parts for Shock Protection.
2.13.4.2 TWO WORKERS
Because of the potential for exposure to energized parts, electrical work, independent of
voltage, that presents a significant shock or arc blast hazard to employees, needs to be
evaluated as to the number of employees involved.
2.13.4.4 ILLUMINATION
Adequate illumination shall be provided before workers are allowed to enter spaces containing
exposed energized parts.
2.13.4.5 SYSTEMS UNDER LOAD
Electrical equipment intended to switch current shall have a rating sufficient for the current.
Manual switches and disconnects, taps, terminators, and nonenclosed switches shall not be
operated while under load, unless the devices are rated as load-break type and are so marked.
2.13.4.6 WORKING WITH TEST INSTRUMENTS AND EQUIPMENT
Sometimes it becomes necessary to check the continuity of power circuits, control circuits, etc.,
by using a particular testing instrument (volt, ohm, and/or amp meter) designed for the testing
involved. The voltage device used shall be rated for the application. Proximity testers and
solenoid-type devices should not be used to test for the absence of voltage because they do not
accurately detect and/or measure voltage. Also, proximity testers will not detect direct current
(DC) or AC voltage in a cable that is shielded. Proximity testers are very useful in certain
applications; for example, for finding cables that go through a panel but that do not terminate in
the panel. However, it should be noted that a proximity tester’s failure to detect voltage does not
guarantee that the equipment or device is deenergized. The absence of voltage can only be
verified with a voltmeter rated for the application.
Voltmeters, both analog and digital, are designed for a number of applications from appliance
troubleshooting to power system testing. The type of voltmeter used depends on where in the
power system you are using the meter. The user must read and understand the manufacturer's
instructions on the use and application of the voltmeter. When a multi-function, multi-scale
meter is used, it is important for the user to select the function and scale necessary for the task
being performed in order to avoid damage or destruction of the meter and injury to the
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employee. The selection of test instruments and equipment shall be based on its application
and categorization.
The following should apply when working with test instruments and equipment on energized
circuits.
2.13.4.6.1 QUALIFIED EMPLOYEES
Only knowledgeable, qualified workers who have been trained to work safely with test
instruments and equipment on energized circuits shall be permitted to perform testing work on
electrical circuits or equipment where there is danger of injury from accidental contact with
energized parts or improper use of the test instruments and equipment.
Section 32
2.13.4.6.2 VISUAL INSPECTIONS
Test instruments and equipment and all associated test leads, cables, power cords, probes, and
connectors shall be visually inspected for external defects or damage before being used on any
shift. If there are defects or evidence of damage that might expose an employee to injury, the
defective or damaged item shall not be used until required repairs and tests have been made.
2.13.4.6.3 RATING INSTRUMENTS AND EQUIPMENT
Test instruments and equipment and their accessories shall be rated for the circuits and
equipment to which they will be connected and shall be suitable for the environment in which
they will be used.
2.13.4.6.4 CALIBRATION OF ELECTRICAL INSTRUMENTS
The American National Standards Institute (ANSI) standard C39.1 defines the minimum
performance and general requirements level for electrical instruments. ANSI standards also
ensure that an instrument, when calibrated to National Institute of Standards and Technology
(NIST) traceable standards, is capable of transferring that quality of measurement to field
conditions within specified limits, where that level of measurement quality is needed.
A record should be maintained for each instrument, by serial number or equivalent method,
showing dates of inspection, calibration data as received, the date when it should be recalled
from the field and a recalibration check made, and any interim repairs. After a period of time, it
should become obvious what frequency needs to be established for calibrating each instrument.
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3.0 ELECTRICAL PREVENTIVE MAINTENANCE
The term "electrical preventive maintenance" (EPM) refers to a program of regular inspection
and service of equipment to detect potential problems and to take proper corrective measures
through the approved work process controls.
3.1 DEVELOPMENT AND IMPLEMENTATION REQUIREMENTS
An EPM program should be developed and implemented based on the requirements of:
1. DOE O 433.1, Maintenance Management Program for DOE Nuclear Facilities (2001)
2. NFPA 70B, Recommended Practice for Electrical Equipment Maintenance (2002)
3. NFPA 70E, Standard for Standard for Electrical Safety in the Workplace (2004)
4. NFPA 72, National Fire Alarm Code (2002)
5. National Electrical Testing Association (1997)
6. ANSI-C2, National Electrical Safety Code (2002)
3.2 DEFINITION
An EPM program is defined as the system that manages the conducting of routine inspections
and tests and the servicing of electrical equipment so that impending troubles can be detected
and reduced or eliminated. Where designers, installers, or constructors specify, install, and
construct equipment with optional auxiliary equipment, that optional equipment should be part of
the EPM program. Records of all inspections, tests, and servicing should be documented and
reviewed.
All electrical equipment that is appropriate for EPM should be inspected, tested, and serviced in
accordance with an EPM program.
Inspections, tests, and servicing shall be performed by personnel who are qualified for the work
to be performed. These qualifications can be shown by appropriate documentation of work
experience, on-the-job, and offsite formal training to verify understanding and retention of
minimum knowledge, skills, and abilities.
3.3 MAINTENANCE
Electrical equipment should be maintained in accordance with the manufacturer's
recommendations and instructions for the local operating environment. A copy of the
manufacturer's recommendations should be documented and on file.
Section 33
3.4 INSPECTION
If an EPM program does not exist, an inspection, testing, and servicing program should be
developed and implemented to establish a baseline to initiate an EPM program. The inspection
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frequency should be as recommended by the manufacturer or as otherwise indicated in NFPA
70B. An initial period of inspection (sometimes several years) provides sufficient knowledge
that, when accumulated, may permit increasing or decreasing that interval based upon
documented observations and experience.
One guidance on how to determine inspection frequency is described in various sections of
NFPA 70B, Tables H.1, H.2, and I.1 including, but not limited to, the following sections:
1. Inspection Frequency for Planning and Developing an Electrical Preventive Maintenance
Program
2. Recommended Frequency for Substations
3. Frequency of Maintenance for Switchgear Assemblies
4. Regular Inspections and Special Inspections and Repairs for Liquid-Filled Transformers
5. Regular Inspections and Special Inspections and Repairs for Dry-Type Transformers
6. Visual Inspection Intervals for Power Cables
7. Frequency of Inspections for Enclosures of Motor Control Centers
8. Recommended Frequency for Ground-Fault Circuit Interrupters
9. General and Inspection and Cleaning for High-Voltage Fuses
10. Frequency for Rotating Equipment
11. Cleaning Interval for Lighting Equipment
12. Visual Inspection Before and After Each Use, Periodic Inspection of Crucial Wear Points,
Excessive Dirt Accumulation, Insufficient or Improper Lubrication, and Visually Inspected
Before Each Use for Portable Electric Tools and Equipment
13. Special Maintenance Tests, Frequency of Tests, Inspection Frequency and Procedures,
and Insulating-Liquid Analysis for Testing and Test Methods
14. Reinspection and Retesting Within One or Two Years After Energization for General
Aspects of Maintaining Medium- and Low-Voltage Distribution Systems, Frequency,
Regreasing, and Frequency for Lubrication of Rotating Equipment
15. Inspections Should Be Made of All New Installations and Whenever Alterations Are
Made and; Recordkeeping for Electrostatics Static Grounding (see NFPA 77)
16. Inspection and Testing of Power Supplies, Functional Systems Testing of Interlock and
Logic Systems, Visual Inspection of Level Devices, Frequency of Testing Safety and
Shutdown Systems, Frequency of Testing Alarm Systems, and Visual Checking of
Wiring Systems for Process Instrumentation and Control
17. Frequency for Cable Tray System
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18. Routine Maintenance for Uninterruptible Power Supply (UPS) Systems
3.5 ESSENTIAL ELEMENTS
The EPM program should include the essential elements described in NFPA 70B, Chapter 5,
What is an Effective EPM Program?. This includes planning, identifying the main parts, and
utilizing available support services for a program. For example:
1. Assigning qualified personnel
2. Surveying and analyzing equipment maintenance requirements
3. Performing routine inspections and tests
4. Analyzing inspection and test reports
5. Prescribing corrective measures
6. Performing necessary work
7. Preparing appropriate records.
3.6 PLANNING AND DEVELOPING AN EPM PROGRAM, AND
FUNDAMENTALS OF EPM
The EPM program should be planned and developed to include each of the functions,
requirements, and economic considerations described in NFPA 70B, Chapter 6, Planning and
Developing an EPM Program, and NFPA 70B, Chapter 7, Fundamentals of EPM. Chapter 6
includes surveying the existing electrical system installation, identifying crucial equipment,
establishing a systematic program to follow, and developing methods and procedures to plan,
analyze, perform, verify, and record.
Section 34
Electrical drawings should be kept current. A system of recording changes in electrical systems
and then integrating those changes into the applicable drawings should be developed and
implemented.
NFPA 70B includes designing to accommodate maintenance, scheduling maintenance,
personnel and equipment safety, circuit protection, and initial acceptance testing.
3.7 GROUND-FAULT PROTECTION
The EPM program should include the essential ingredients of Chapter 14 of NFPA 70B, Ground
Fault Protection. This includes GFCls and ground-fault protection for equipment (GFPE).
Ground-fault protective devices are intended to protect personnel and equipment. There are two
distinct types — GFCI and GFPE — and it is extremely important to understand the difference
between them.
A GFCI is defined in Article 100 of the NEC as a device intended for the protection of personnel
in their job assignments. (See NEC 210.8, 215.9, 427, 527)
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A GFPE is defined in Article 100 of the NEC as a system intended to provide protection of
equipment from line-to-ground fault currents. GFPE systems (equipped with or without a test
panel) shall be inspected and tested at installation and at specified intervals as recommended
by the manufacturer.
Figure 3-1 shows a zero-sequence type of ground fault protection.
Inspections, tests, and servicing shall be performed by personnel who are qualified for the work
to be performed. These qualifications can be shown by appropriate documentation of work
experience, on-the-job, and offsite formal training to verify understanding and retention of
minimum knowledge, skills, and abilities.
Figure 3-1. Ground-fault protection shall be provided with 277/480-V, three-phase,
four-wire services with over current protection devices of 1,000 A or more. A ground
fault sensor (window) can be used to encircle all service conductors, including the
grounded conductor (neutral).
• NEC 230.95
• NEC 230.95 (A)
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4.0 GROUNDING
This section presents general rules for the grounding and bonding of electrical installations.
Qualified workers should clearly understand the concepts of grounding practices as required by
the NEC. They should also clearly understand the definition and intent of the following
components of a grounding system that are explained in this chapter:
1. Grounded conductor
2. Grounding conductor
3. Grounding electrode conductor
4. Bonding jumper
5. Grounding electrode
4.1 REGULATIONS, CODES, AND REFERENCES
4.1.1 ENGINEERING SPECIFICATIONS AND DRAWINGS
Engineering specifications and drawings should identify the requirements for all components
and clearly illustrate the grounding electrode system, the grounding electrode conductor,
bonding points and bonding jumpers, and the connection point for the grounded conductor and
the grounding conductors. Where used for installation or construction purposes, these
specifications and drawings should also include detailed installation instructions.
4.2 CIRCUIT AND SYSTEM GROUNDING
Circuit and system grounding consists of connecting the grounded conductor, the equipment
grounding conductor, the grounding bus bars, and all noncurrent-carrying metal parts to ground.
This is accomplished by connecting a properly sized unspliced grounding electrode conductor
between the grounding bus bar and the grounding electrode system. There are three
fundamental purposes for grounding an electrical system:
Section 35
1. To limit excessive voltage from lightning, line surges, and crossovers with higher voltage
lines.
2. To keep conductor enclosures and noncurrent-carrying metal enclosures and equipment at
zero potential to ground.
3. To facilitate the opening of overcurrent protection devices in case of insulation failures
because of faults, short circuits, etc.
4.3 EQUIPMENT GROUNDING
Equipment grounding systems, which consist of interconnected networks of equipment
grounding conductors, are used to perform the following functions:
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1. Limit the hazard to personnel (shock voltage) from the noncurrent-carrying metal parts of
equipment raceways and other conductor enclosures in case of ground faults, and
2. Safely conduct ground-fault current at sufficient magnitude for fast operation of the circuit
overcurrent protection devices.
To ensure the performance of the above functions, equipment grounding conductors are
required to:
1. Be permanent and continuous
2. Have ample capacity to safely conduct ground-fault current likely to be imposed on them;
and
3. Have impedance sufficiently low to limit the voltage to ground to a safe magnitude and to
facilitate the operation of the circuit overcurrent protection devices.
4.4 BONDING
Caution shall be taken to ensure that the main bonding jumper and equipment bonding jumper are
sized and selected correctly. Bonding completes the grounding circuit so that it is continuous. If a
ground fault occurs, the fault current will flow and open the overcurrent protection devices. The
means of bonding shall provide the following to ensure the grounding system is intact:
1. Provide a permanent connection,
2. Provide a positive continuity at all times, and
3. Provide ampacity to conduct fault current.
See Figure 4-1 on the proper grounding of electrical systems.
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Electrical systems can be operated grounded or ungrounded, depending on the condition of
their use. Electrical systems are grounded to protect circuits, equipment, and conductor
enclosures from dangerous voltages and personnel from electrical shock.
4.5 GROUNDED OR UNGROUNDED SYSTEMS
Ungrounded systems may provide greater continuity of operations in the event of a fault.
However, the second fault will most likely be more catastrophic than a grounded system fault.
Whenever ungrounded systems are used in a facility, the maintenance personnel should
receive training in how to detect and troubleshoot the first fault on an ungrounded system.
"Grounded" means that the connection to ground between the service panel and earth has been
made. Ungrounded electrical systems are used where the designer does not want the
overcurrent protection device to clear in the event of a ground fault.
Ground detectors can be installed per NEC to sound an alarm or send a message to alert
personnel that a first fault has occurred on one of the phase conductors. Ground detectors will
detect the presence of leakage current or developing fault current conditions while the system is
still energized and operating. By warning of the need to take corrective action before a problem
occurs, safe conditions can usually be maintained until an orderly shutdown is implemented.
Figure 4-1. Circuit and system grounding consists of earth grounding the electrical
system at the supply transformer and the line side of the service equipment. Equipment
grounding and bonding is accomplished by connecting all metal enclosures and
raceways together with the grounding conductors.
Section 36
NEC 250.4
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4.5.1 GROUNDED SYSTEMS
Grounded systems are equipped with a grounded conductor that is required to be run to each
service disconnecting means. The grounded conductor can be used as a current-carrying
conductor to accommodate all neutral related loads. It can also be used as an equipment
grounding conductor to clear ground faults ahead of the service disconnecting means.
A network of equipment grounding conductors is routed from the service equipment enclosure
to all metal enclosures throughout the electrical system. The equipment grounding conductor
carries fault currents from the point of the fault to the grounded bus in the service equipment
where it is transferred to the grounded conductor. The grounded conductor carries the fault
current back to the source and returns over the faulted phase and trips open the overcurrent
protection device.
Note: A system is considered grounded if the supplying source, such as a transformer or
generator is grounded in addition to the grounding means on the supply side of the service
equipment disconnecting device for separately derived systems.
The neutral of any grounded system serves two main purposes: (1) it permits the utilization of
line-to-neutral voltage and thus will serve as a current-carrying conductor to carry any neutral
current, and (2) it plays a vital role in providing a low-impedance path for the flow of fault
currents to facilitate the operation of the overcurrent devices in the circuit. (See Figure 4-2.)
Consideration should be given to the sizing of the neutral conductor for certain loads due to the
presence of harmonic currents.
NEC 250.130
Figure 4-2. A grounded system is equipped with a grounded (neutral) conductor
routed between the supply transformer and the service equipment.
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4.5.2 UNGROUNDED SYSTEMS
Ungrounded systems operate without a grounded conductor. In other words, none of the circuit
conductors of the electrical system are intentionally grounded to an earth ground such as a
metal water pipe, or building steel. The same network of equipment grounding conductors is
provided for ungrounded systems as for solidly grounded electrical systems. However,
equipment grounding conductors (EGCs) are used only to locate phase-to-ground faults and
sound some type of alarm. Therefore, a single sustained line-to-ground fault does not result in
an automatic trip of the overcurrent protection device. This is a major benefit if electrical system
reliability is required or if it would result in the shutdown of a continuous process. However, if an
accidental ground fault occurs and is allowed to flow for a substantial time, overvoltages can
develop in the associated phase conductors. Such an overvoltage situation can lead to
conductor insulation damage, and while a ground fault remains on one phase of an ungrounded
system, personnel contacting one of the other phases and ground are subjected to 1.732 times
the voltage they would experience on a solidly neutral grounded system. (See Figure 4-3.)
Note: All ungrounded systems should be equipped with ground detectors and proper
maintenance applied to avoid, to the extent practical, the overcurrent of a sustained ground fault
on ungrounded systems. If appropriate maintenance is not provided for ungrounded systems, a
grounded system should be installed to ensure that ground faults will be cleared and circuits,
equipment, and personnel are safe.
4.5.3 HIGH-IMPEDANCE GROUNDING
Section 37
Electrical systems containing three-phase, three-wire loads, as compared to grounded neutral
circuit conductor loads, can be equipped with a high-impedance grounded system. High-
impedance grounded systems shall not be used unless they are provided with ground fault
Figure 4-3. An ungrounded system does not have a grounded (neutral) conductor
routed between the supply transformer and the service equipment because the supply
transformer is not earth grounded.
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indicators or alarms, or both, and qualified personnel are available to quickly locate and eliminate
such ground faults. Ground faults must be promptly removed or the service reliability will be
reduced. See NEC for requirements on installing a high-impedance grounding system. (See
Figure 4-4.)
4.6 GROUNDING REQUIREMENTS
Alternating current systems of less than 50 volts shall be grounded as required in NEC.
Systems of 50 to 1,000 V should be solidly grounded as required by NEC. Systems supplying
phase-to-neutral loads shall also be solidly grounded (See Figure 4-5). The following electrical
systems are required to be solidly grounded:
1. 240/120-V, single-phase, three-wire
2. 208Y/120-V, three-phase, four-wire
3. 480Y/277-V, three-phase, four-wire
4. 240/120-V, three-phase, four-wire, delta (midpoint of one phase used as a
grounded circuit conductor)
The following systems are not required to be solidly grounded:
Figure 4-4. A high-impedance grounding system has a high-impedance unit, installed
between the grounded (neutral) conductor and the grounding electrode conductor,
which is used to regulate fault current.
NEC 250.36
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1. 240-V, three-phase, three-wire delta
2. 480-V, three-phase, three-wire
3. 600-V, three-phase, three-wire.
These electrical systems do not supply phase-to-neutral loads. They supply only phase-to-
phase loads.
4.7 GROUNDING ELECTRODE CONDUCTOR (GEC)
The main purpose of the grounding electrode conductor (GEC) is to connect the electrical
system to earth ground. The GEC actually provides three grounding paths to the grounding
electrode system. They are as follows:
1. The grounded conductor path
2. The equipment grounding path
3. The bonding path
NEC 250.20
Figure 4-5. Systems of 50 to 1,000 V AC that operate grounded are required to have the
grounded conductor connected to earth ground at the supplying transformer and
service equipment.
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In grounded systems, the GEC connects to the neutral bar in the service equipment enclosure.
In ungrounded systems, the GEC connects to the grounding terminal bar. It grounds the
following items to the grounding electrode system:
1. The grounded conductor, if present
2. The equipment grounding conductor, if present
3. The metal of conduits, if present
4. The metal of enclosures, if present
5. The bonding jumpers bonding together metal enclosures and conduits
6. The metal enclosure of the service equipment
4.7.1 SIZING THE GROUNDING ELECTRODE CONDUCTOR
NEC 250.66 requires the grounding electrode conductor to be sized by the circular mils rating of
the largest service entrance conductor or conductors and selected from NEC Table 250.66
based on these values.
For example, the size of the service entrance conductors from a delta, three-phase, four-wire
midpoint tap is #250 kcmil, THWN copper for phases A and C, #2/0 for phase B, and #1/0 for
the neutral. What size copper GEC is required to ground this system to a metal water pipe?
Section 38
Note: NEC Table 250.66 is used to size the grounding electrode conductor for both grounded
and ungrounded systems. The table is used where the grounding electrode conductor is
connected to a metal water pipe or the metal frame of building steel.
4.7.2 EXCEPTIONS TO NEC 250.66
There is an exception to the main rule. It has three parts and pertains to specific types of
grounding electrodes. The exception applies to grounded and ungrounded systems.
Exception (A) applies to made electrodes only, such as rod, pipe, or plate electrodes. The
grounding electrode conductor is not required to be larger than #6 copper or #4 aluminum.
Exception (B) to NEC 250.66 requires at least a #4 copper conductor to be used as a grounding
electrode conductor to ground the electrical system to a concrete-encased electrode.
Exception (C) requires at least a #2 copper conductor to be used as a grounding electrode
conductor to ground the electrical system to a ground ring.
Step 1: Finding the largest phase-NEC 250.66 #250 kcmil is the largest phase
Step 2: Finding the size GEC-NEC Table 250.66 #250 kcmil requires #2 cu
Answer: The size of grounding electrode conductor (GEC) is at least #2 copper.
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4.8 MAIN BONDING JUMPER
The primary function of the main bonding jumper is to connect the grounded circuit conductors
and the equipment grounding conductors at the service equipment. The main bonding jumper
serves as the main link between the system grounded conductors and the grounding electrode
system where metal equipment enclosures and raceways are utilized to enclose conductors and
components. If the main bonding jumper is left out, there is no complete circuit for fault current,
which poses a potentially dangerous situation.
The main bonding jumper shall connect together the following items:
1. Grounded conductors and grounded terminal
2. Equipment grounding conductors and grounding terminal
3. All metal enclosures enclosing conductors and components.
If supplied, the manufacturer’s main bonding jumper is the preferred conductor to be used as
the main bonding jumper. NEC requires the main bonding jumper to be a (1) wire, (2) screw, (3)
bus bar, or (4) a similar suitable conductor.
NEC requires the main bonding jumper to be at least the same size as the grounding electrode
conductor where the circular mils rating of the service entrance conductors does not exceed
1100 kcmil for copper or 1750 kcmil for aluminum.
For example: What size main bonding jumper is required to ground the metal enclosure of the
service equipment to the grounding terminal bar where the service entrance is made up of one
#250 kcmil, THWN copper conductor per phase?
For example: What size main copper bonding jumper is required for a service entrance with a
makeup of 2400 kcmil copper conductors per phase?
Note: In this case the main bonding jumper is greater in size than the grounding electrode
conductor, which is only required to be #3/0 copper per NEC Table 250.66 based upon the 2400
kcmil copper conductors.
Step 1: Finding the largest phase — NEC 250.28 #250 kcmil is the largest phase
Step 2: Finding the bonding jumper — Table 250.66 #250 kcmil requires #2 copper
Answer: The size of the main bonding jumper (GEC) is at least #2 copper.
Step 1: Finding the largest phase — NEC 250.28, 2400 kcmil x 0.125 = 300 kcmil
Step 2: Finding the main bonding jumper — NEC Table 250.66, requires 300 kcmil
Answer: The main bonding jumper is required to be at least 300 kcmil copper.
Section 39
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4.9 SYSTEM WITH GROUNDED CONDUCTOR
The main purpose of the grounded conductor is to carry unbalanced neutral current or fault
current in the event that one phase should go to ground.
Note: The grounded conductor does not always have to be a neutral conductor. It can be a
phase conductor, as when used in a corner grounded delta system.
In solidly grounded service-supplied systems, the equipment grounding conductors shall be
bonded to the system-grounded conductor and the grounding electrode conductor at the service
equipment. The grounded conductor may be used to ground the noncurrent-carrying metal parts
of equipment on the supply side of the service disconnecting means per NEC 250.142. The
grounded conductor can also serve as the ground-fault current return path from the service
equipment to the transformer that supplies the service.
The grounded conductor shall not be used to ground the metal parts of enclosures enclosing
conductors and components on the load side of the service per NEC 250.142. See NEC
250.182, 250.130 and 250.140 for exceptions to this basic rule. NEC 250.24 requires the
grounded conductor to be connected as follows:
1. The grounded conductor shall be connected to the grounded (neutral) service conductor.
2. The connection shall be at an accessible point.
3. That accessible point can be anywhere from the load end of the service drop or service
lateral to and including the neutral bar in the service disconnecting means or service
switchboard.
The NEC allows the grounded conductor to be terminated and connected to ground at a
multitude of locations on the supply side of the service equipment. These locations are as
follows:
1. Service equipment
2. Meter base
3. Current transformer (CT) can
4. Metal gutter or wire way containing service entrance conductors.
See Figure 4-6 for the rules concerning the use of the grounded conductor.
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NEC 250.24 lists the rules for sizing the grounded conductor where it is not used as a grounded
neutral circuit. NEC gives the rules for calculating and sizing the grounded conductor when it is
used as a circuit conductor. The minimum size for the grounded conductor is computed as
follows:
1. The basic rule is to select the size directly from NEC Table 250.66 when the size of the
service-entrance conductors is not larger than 1100 kcmil copper or 1750 kcmil aluminum.
2. When the service entrance conductors are larger than 1100 kcmil copper or 1750 kcmil
aluminum, the grounded conductor shall be 12½ percent of the largest phase conductor.
3. Where the service phase conductors are paralleled, the size of the grounded conductor
shall be based on the total cross-sectional area of the phase conductors.
For example: What size THWN copper grounded conductor is required for a service having a
total kcmil rating of 250 per phase? (All phase conductors are THWN copper)
Step 1: Service less than 1100 kcmil - NEC Table 250.66, 250 kcmil requires #2
copper
Answer: The size of the grounded conductor is at least #2 THWN copper.
NEC 250.24(b)
Figure 4-6. The grounded (neutral) conductor is used to carry normal neutral current
or ground fault current in case a ground fault should develop on one of the
ungrounded (hot) phase conductors.
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For example: What size THWN copper grounded conductor is required for a parallel service
having a total kcmil rating of 2400 per phase? (All conductors are THWN copper)
Section 40
Note: NEC Table 250.66 is used only if the service conductors are rated less than 1100 kcmil
for copper or 1750 kcmil for aluminum.
4.10 EQUIPMENT GROUNDING CONDUCTOR
Equipment grounding conductors for ac systems, where used, should be run with the
conductors of each circuit per NEC 250.119, and 250.134.
Earth and the structural metal frame of a building may be used for supplemental equipment
bonding, but they shall not be used as the sole equipment grounding conductor for ac systems.
For circuits having paralleled conductors in multiple metal raceways, an equipment grounding
conductor shall be run in each raceway. Each paralleled equipment grounding conductor must
be full size based on the circuit overcurrent protection. (See NEC 250.122)
4.10.1 SIZING THE EQUIPMENT GROUNDING CONDUCTOR
NEC 250.122 lists the requirements for calculating the size of the equipment grounding
conductors in an electrical circuit. There are basically five steps to be applied in sizing,
selecting, and routing the equipment grounding conductors:
This method is used where the service entrance conductors are over 1100 kcmil copper or
1750 kcmil aluminum. NEC Table 250.66 cannot be used for sizing the grounded conductor.
The grounded conductor is required to be not less than 12½ percent of the cross-sectional area
of the largest phase conductor.
1. NEC Table 250.122 shall be used to size the equipment grounding conductor.
2. When conductors are run in parallel in more than one raceway, the equipment grounding
conductor is also run in parallel.
3. Where more than one circuit is installed in a single raceway, one equipment grounding
conductor may be installed in the raceway. However, it must be sized for the largest
overcurrent device protecting conductors in the raceway.
4. When conductors are adjusted in size to compensate for voltage drop, the equipment
grounding conductor shall also be adjusted in size.
5. The equipment grounding conductor is never required to be larger than the circuit
conductors.
Step 1: Service exceeding 1100 kcmil - NEC Table 250.66, 2400 kcmil x 0.125 = 300
kcmil
Answer: The grounded conductor is required to be at least a #300 kcmil, THWN copper
conductor.
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For example: What size THWN copper equipment grounding conductor is required to be run in a
raceway with a 70 A overcurrent protection device protecting the circuit?
4.10.2 SEPARATE EQUIPMENT GROUNDING CONDUCTORS
The possibility of worker exposure to electric shock can be reduced by the use of separate
equipment grounding conductors within raceways.
The separate equipment grounding conductors contribute to equalizing the potential between
exposed noncurrent-carrying metal parts of the electrical system and adjacent grounded
building steel when ground faults occur. The resistance (inductive reactance) of the ground fault
circuit normally prevents a significant amount of ground fault current from flowing through the
separate equipment grounding conductors.
Ground fault current flows through the path that provides the lowest ground fault circuit
impedance. Fittings and raceway systems have been found that are not tightly connected or are
corroded which prevents good continuity. Therefore, the equipment grounding conductor shall
be the path for the fault current to travel over and clear the overcurrent protection device
protecting the circuit.
Section 41
NEC 250.134(B) requires the equipment grounding conductors to be routed in the same
raceway, cable, cord, etc., as the circuit conductors. All raceway systems should be
supplemented with separate equipment grounding conductors.
Note: The equipment grounding conductor shall be routed with supply conductors back to the
source. Additional equipment grounding may be made to nearby grounded structural members
or to grounding grids, but this shall not take the place of the co-routed equipment grounding
conductors. Raceway systems should not be used as the sole grounding conductor.
4.11 UNGROUNDED SYSTEMS
Three-phase, three-wire, ungrounded systems (delta), which are extensively used in industrial
establishments, do not require the use of grounded conductors as circuit conductors.
The same network of equipment grounding conductors shall be provided for ungrounded
systems as for grounded systems. Equipment grounding conductors are required in ungrounded
systems to provide shock protection and to present a low-impedance path for phase-to-phase
fault currents in case the first ground fault is not located and cleared before another ground fault
occurs on a different phase in the system.
Grounding electrode conductors and bonding jumpers shall be computed, sized, and installed in
the same manner as if the system were a grounded system. Apply all the requirements listed in
Sections 4.6 through 4.8 for sizing the elements of an ungrounded system.
Step 1: Finding EGC - NEC Table 250.122, 70 A OCPD requires #8 copper
Answer: The equipment grounding conductor is required to be at least #8 THWN copper.
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4.12 GROUNDING A SEPARATELY DERIVED SYSTEM
NEC 250.30 covers the rules for grounding separately derived systems. The system grounding
conductor for a separately derived system shall be grounded at only one point. That single
system grounding point is at the source of the separately derived system and ahead of any
system disconnecting means or overcurrent devices. Where the main system disconnecting
means is adjacent to the generator, converter, or transformer supplying a separately derived
system, the grounding connection to the system grounded conductor can be made at or ahead
of the system disconnecting means.
The preferred grounding electrode for a separately derived system is the nearest effectively
grounded structural metal member of the building or the nearest effectively grounded water
pipe. If neither is available, concrete-encased electrodes or made electrodes are permitted.
In a grounded, separately derived system, the equipment grounding conductors shall be bonded
to the system-grounded conductor and to the grounding electrode at or ahead of the main
system disconnecting means or overcurrent protection device. The equipment grounding
conductor should always be connected to the enclosure of the supply transformer, generator, or
converter.
The grounding electrode conductor, the main bonding jumper, the grounded conductor, and the
equipment grounding conductor are calculated, sized, and selected by the rules listed in
Sections 4.7 through 4.10. (See Figure 4-7.)
Figure 4-7. The grounded (neutral) conductor can be used to carry both normal neutral
current and abnormal ground fault current.
DOE-HDBK-1092-2004
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4.13 GROUNDING ELECTRODE SYSTEM
Section 42
If 10 feet or more of metal water pipe is in the earth, the water pipe is considered the grounding
electrode, but it shall be supplemented by an additional electrode. NEC 250.50 lists four types
of electrodes. If one or all are available, they shall be bonded together to make up the grounding
electrode system. The bonding jumper that connects these electrodes shall be at least as large
as the grounding electrode conductor of the system sized by NEC Table 250.66. The four types
of electrodes are as follows:
1. Metal water pipe in contact with the earth for 10 feet or more. Interior metal water pipe
beyond 5 feet from the water entrance shall not be used as a part of the grounding
electrode system or as a conductor to interconnect those electrodes.
2. Metal frame of the building, where effectively grounded
3. Bare #4 conductor at least 20 feet in length and near the bottom of the concrete foundation
(within 2 inches), or ½-inch reinforcing steel or rods at least 20 feet in length (one
continuous length or spliced together)
4. Bare #2 conductor encircling building at least 2½ feet in the ground (spliced together at
each end).
The grounding electrode conductor at the service equipment can be connected to any
convenient interbonded electrodes that provide a solid, effective connection. Metal water pipe
shall be supplemented by an additional electrode, which can be any of the following electrodes:
1. Rod
2. Pipe
3. Plate
4. Building steel
5. Concrete-encased electrode.
(See Figure 4-8, which lists some of the different types of grounding electrodes.)
DOE-HDBK-1092-2004
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4.14 GROUND-FAULT PROTECTION OF EQUIPMENT
See Section 2.7 for GFCIs for personnel protection. An increased degree of protection in solidly
grounded systems can be achieved in providing ground-fault protection that will shunt trip circuit
protective devices when user-selected levels of ground fault or leakage current flow are
detected in electrical circuits. This is required to be installed on all solidly grounded wye
services of more than 150 V to ground but not exceeding 600 V phase-to-phase where the
service disconnecting means is rated at 1,000 A or more (See Figure 3-1).
4.15 PERSONNEL PROTECTIVE GROUNDS
Personnel working on or close to deenergized lines or conductors in electrical equipment should
be protected against shock hazard and flash burns that could occur if the circuit were
inadvertently reenergized. Properly installed equipotential protective grounds can aid in
lessening such hazards by providing additional protection to personnel while they service,
repair, and work on such systems. (See Section 7.5).
4.15.1 PURPOSE OF PERSONNEL PROTECTIVE GROUNDS
Personnel protective grounds are applied to deenergized circuits to provide a low-impedance
path to ground should the circuits become reenergized while personnel are working on or close
to the circuit. In addition, the personnel protective grounds provide a means of draining off static
and induced voltage from other sources while work is being performed on a circuit (Figure 4-9
illustrates an example of a personnel protective ground).
Figure 4-8. If the building steel, metal water pipe, concrete-encased electrode, and
ground ring are available, they must be grounded and bonded to the service
equipment to create the grounding electrode system.
DOE-HDBK-1092-2004
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4.15.2 CRITERIA FOR PERSONNEL PROTECTIVE GROUNDS
Before personnel protective grounds are selected, the following criteria shall be met for their
use, size, and application.
Section 43
1. A grounding cable shall have a minimum conductance equal to #2 American Wire Gage
(AWG) copper.
2. Grounding cables shall be sized large enough to carry fault current long enough for the
protective devices to sense and the circuit breaker to clear the fault without damage to
cable insulation. An example would be a 4/0 Neoprene-insulated welding cable that will
pass 30,000 A for 0.5 sec without melting its insulation.
3. The following are factors that contribute to adequate capacity:
a. Terminal strength depends on the ferrules installed on the cable ends
b. Cross-sectional area to carry maximum current without melting
c. Low resistance to keep voltage drop across the areas in which personnel are
working at a safe level during any period to prevent reenergization. The voltage drop
should not exceed 100 volts for 15-cycle clearing times or 75 volts for 30-cycle
clearing times.
d. Verify that the grounding cable and clamp assembly is tested periodically by using
the millivolt drop, micro-ohm meter, AC resistance, or DC resistance test methods.
For example, if it is desired to maintain a maximum of 100 volts across a worker
whose body resistance is 1000 ohms, during a fault of 1000 amperes, a personnel
protective ground resistance of 10 milliohms or less is required.
Figure 4-9. Equipotential personnel protective grounds are used to protect electrical
workers while they service, repair, or are close to circuits that can be accidentally
reenergized.
DOE-HDBK-1092-2004
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4. For further information on the construction of personnel protective grounds, refer to
Section 7.5.
4.15.3 GROUNDING CLAMPS
Grounding clamps used in personnel protective grounds are manufactured specifically for this
use. The size of grounding clamps shall match the size of conductor or switchgear bus being
grounded.
The ground clamp also shall be rated to handle the full capacity of the available fault currents.
Fault currents can typically range in magnitude up to over 200,000 A.
4.15.4 SCREW-TIGHTENING DEVICES
Approved screw-tightening devices designed for the purpose of pressure metal-to-metal contact
are required for connections to an adequate system ground.
4.15.5 GROUNDING CABLE LENGTH
Grounding cables should be no longer than is necessary, both to minimize voltage drop and to
prevent violent movement under fault conditions. For example, as a general rule, grounding
cables should not exceed 30 feet for a transmission line and 40 feet for substation use.
4.15.6 GROUNDING CABLE CONNECTION
Grounding cables shall be connected between phases to the grounded structure and to the
system neutral to minimize the voltage drop across the work area if the circuit should become
inadvertently reenergized. Workers shall install the ground end clamp of a grounding cable first
and remove it last.
4.15.7 CONNECTING GROUNDING CABLES IN SEQUENCE
Grounding cables shall be connected to the ground bus, structure, or conductor first, then to the
individual phase conductors. The first connection of the grounding cables to the circuit phase
conductors shall be to the closest phase of the system and then to each succeeding phase in
the order of closeness.
4.15.8 REMOVING PROTECTIVE GROUNDS
When removing personnel protective grounds, reverse the order they were applied to the
phases. The grounding cable conductors attached to the ground bus, structure, or conductors
shall always be removed last.
4.15.9 PROTECTIVE APPAREL AND EQUIPMENT
Section 44
Protective apparel shall be worn when applying or removing grounds. An insulating tool (hot
stick) shall be used to install and remove grounding cables.
Protective apparel (PPE) should include at least the following:
1. Safety glasses and, if necessary, a face shield appropriate for existing fault currents.
DOE-HDBK-1092-2004
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2. Hardhat (Class B) (See 2.12)
3. Appropriate electrical gloves and protectors (See 2.12).
4. Appropriate clothing (See 2.12).
DOE-HDBK-1092-2004
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5.0 SPECIAL OCCUPANCIES
This section covers the specific requirements and information for installing electrical equipment
and wiring in explosive and hazardous locations and underground facilities. Classifications of
areas or locations with respect to hazardous conditions are discussed. Information is provided
on the correct methods and techniques needed for system grounding, lightning protection, and
controlling of static electricity.
This section references DOE, NFPA, and Department of Defense (DoD) standards. These
standards and manuals should be referenced to ensure safe and reliable installations of
electrical equipment and wiring methods in explosive and hazardous locations.
5.1 EXPLOSIVES
This section references DOE M 440.1-1, DOE Explosives Safety Manual, NFPA 70 (NEC),
NFPA 77, NFPA 780, and DoD 6055.9-STD, DoD Ammunition and Explosives Safety
Standards. These standards and manuals should be referenced to ensure safe and reliable
installations of electrical equipment and wiring methods in explosive and hazardous locations.
5.1.1 EVACUATION
Whenever an electrical storm approaches, personnel shall exit any location where a hazard
exists from explosives being detonated by lightning. Evacuation may be necessary from
locations listed below:
1. All outdoor locations, locations in buildings that do not have lightning protection, and
locations within inhabited building distance of the hazard. (When an electrical storm is
imminent, work with explosives operations shall not be undertaken.)
2. Locations (with or without lightning protection) where operations use electrostatic-sensitive
bulk explosives or electroexplosive devices (EEDs).
5.1.2 SHUTDOWN OF OPERATIONS
The following guidelines shall be used for shutdown of an operation during an electrical storm:
1. Process equipment containing explosives shall be shut down as soon as safety permits.
2. When buildings or bays containing explosives are evacuated, functions that cannot be shut
down immediately shall be operated by the minimum number of personnel required for safe
shutdown. When the operation has been brought to a safe condition, those remaining shall
evacuate.
3. Automatic emergency power equipment shall be provided if electrical power is critical to an
explosives operation during a power shutdown or interruption.
5.1.3 LIGHTNING PROTECTION
It is DOE policy to install lightning protection on all facilities used for storage, processing, and
handling of explosive materials where operations cannot be shut down and personnel
DOE-HDBK-1092-2004
5-2
evacuated during electrical storms. Specific operations shall be assessed for the risk of
detonation of explosives by lightning. Such assessment shall consider the need for the
protection factors outlined in Appendix I, NFPA 780. When risk is high, as in operations with
highly sensitive electrostatic materials or components, operations shall be conducted only in
lightning-protected facilities. Approved lightning protection systems shall conform with the
requirements of Appendix I, NFPA 780.
Section 45
Lightning-protection systems should be visually inspected every 7 months and a report on their
conditions filed at least annually. Any evidence of corrosion, broken wires or connections, or any
other problem that negates the system's usefulness shall be noted and the problem repaired.
Lightning protection systems should be tested electrically every 14 months to ensure testing
during all seasons, or immediately following any repair or modification. The testing shall be
conducted only with instruments designed specifically for earth-ground system testing. The
instruments shall be able to measure 10 ohms ±10% for ground resistance testing and 1 ohm
±10% for bonding testing. Electrical resistance readings shall be recorded.
Inspection records shall contain the most recent electrical test report and any subsequent visual
inspection reports for each building with a lightning-protection system.
5.1.4 STATIC ELECTRICITY
Static electricity shall be controlled or eliminated in areas where materials are processed or
handled that are ignitable by static spark discharge. This category includes spark-sensitive
explosives, propellants, and pyrotechnics, as well as solvent vapors and flammable gases.
Approved systems to dissipate static electricity shall conform to the requirements of NFPA 77
and IEEE 142.
5.1.4.1 BONDING AND GROUNDING EQUIPMENT
Bonding straps shall be used to bridge locations where electrical continuity may be broken by
the presence of oil on bearings, or by paint or rust at any contact point. Permanent equipment in
contact with conductive floors or tabletops is not considered adequately grounded. Static
grounds shall not be made to gas, steam, or air lines; dry-pipe sprinkler systems; or air
terminals of lightning protection systems. Any ground that is adequate for power circuits or
lightning protection is more than adequate for protection against static electricity.
5.1.4.2 TESTING EQUIPMENT GROUNDING SYSTEMS
Grounding systems shall be tested for electrical resistance and continuity when installation is
complete and, in the case of active equipment, at intervals to be locally determined. The
grounding system shall be visually inspected for continuity before it is reactivated if the
equipment has been inactive for more than 1 month. All exposed explosives or hazardous
materials shall be removed before testing. During a test for resistance to ground, all equipment,
except belt-driven machines, shall be considered as a unit. In measuring the total resistance to
ground for belt-driven machinery (to ensure compliance with Section 5.1.4.3), resistance of the
belt is to be excluded. All conductive parts of equipment shall be grounded so that resistance
does not exceed 25 ohms, unless resistance is not to exceed 10 ohms because of the lightning
protection system. For existing equipment, the rate of static electricity generation shall be
considered before changes are made in grounding systems. The resistance of conductive
rubber hose shall not exceed 250,000 ohms.
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5.1.4.3 CONDUCTIVE FLOORS, SHOES, MATS, AND WRISTBANDS
Conductive floors and shoes should be used for grounding personnel conducting operations
involving explosives that have an electrostatic sensitivity of 0.1 joule or less. Many flammable
liquids and air mixtures can be ignited by static discharge from a person. In areas where
personnel come close enough to have possible contact with static-sensitive explosives or
vapors, conductive floors shall be installed except where the hazards of dust-air or flammable
vapor-air mixtures are eliminated by adequate housekeeping, dust collection, ventilation, or
solvent-recovery methods. Conductive floors may also be required where operations are
performed involving EEDs that contain a static-sensitive explosive.
Section 46
Conductive floors are not required throughout a building or room if the hazard remains localized.
In such cases, conductive mats or runners may suffice. These mats or runners shall be subject
to all the specifications and test requirements that apply to conductive floors. Conductive
wristbands may be substituted for conductive mats and footwear at fixed, grounded
workstations or outdoor location.
5.1.4.4 SPECIFICATIONS FOR CONDUCTIVE FLOORS AND WRISTBANDS
Conductive floors shall be made of nonsparking materials such as conductive rubber or
conductive flooring material and shall meet the following requirements:
1. The flooring and its grounding system shall provide for electrical resistance not to exceed
1,000,000 ohms (measured as specified in Section 5.1.4.5).
2. The surface of the installed floor shall be reasonably smooth and free from cracks. The
material shall not slough off, wrinkle, or buckle under operating conditions. Conductive tiles
are not recommended for use in areas where contamination can be caused by explosive
dust. The large number of joints and the tendency of tiles to loosen provide areas where
explosive dust can become lodged and that are not easy to clean with normal cleaning
procedures.
3. Where conductive floors and shoes are required, resistance between the ground and the
wearer shall not exceed 1,000,000 ohms, which is the total resistance of conductive shoes
on a person plus the resistance of floor to ground. Where conductive floors and shoes are
required, tabletops on which exposed explosives or dust are encountered shall be covered
with a properly grounded conductive material meeting the same requirements as those for
flooring.
4. Conductive floors shall be compatible with the explosive materials to be processed.
5. Conductive wristbands shall not exceed a resistance of 1,000,000 ohms between the wearer
and ground. This resistance shall be measured with a suitably calibrated ohmmeter.
Wristbands shall be of a design that maintains electrical contact with the wearer when
tension is applied to the ground lead wire or the wristband is placed under strain.
5.1.4.5 CONDUCTIVE FLOOR TEST
Before use, tests shall be conducted on all conductive floors; subsequent tests shall be made at
least semiannually. Test results shall be permanently recorded and a copy filed in a central
DOE-HDBK-1092-2004
5-4
location. Instruments used in testing shall be used only when the room is free from exposed
explosives and mixtures of flammable gases.
Maximum floor resistance shall be measured with a suitably calibrated insulation resistance
tester that operates on a normal open-circuit output voltage of 500 V dc and a short-circuit
current of 2.5 mA with an effective internal resistance of approximately 200,000 ohms. Minimum
floor resistance shall also be measured with a suitably calibrated ohmmeter.
Each electrode shall weigh 2.3 kg and shall have a dry, flat, circular contact area 6½ cm in
diameter, which shall comprise a surface of aluminum or tinfoil 1.3 to 2.5 mm thick, backed by a
layer of rubber 0.6 to 0.65 cm thick, and measuring between 40 and 60 durometer hardness as
determined with a Shore Type A durometer.
The floor shall be clean and dry. Only electrode jelly shall be used to establish a good contact.
(Brushless shaving soap and saline solution shall not be used.)
Section 47
The resistance of the floor shall be more than 5,000 ohms in areas with 110-V service, 10,000
ohms in areas with 220-V service, and less than 1,000,000 ohms in all areas, as measured
between a permanent ground connection and an electrode placed at any point on the floor and
also as measured between two electrodes placed 3 ft apart at any points on the floor.
Measurements shall be made at five or more locations in each room. If the resistance changes
appreciably during a measurement, the value observed after the voltage has been applied for
about 5 sec shall be considered the measured value. (See Figure 5-1.)
5.1.4.6 HUMIDIFICATION
Humidification to prevent accumulations and subsequent discharges of static electricity is
usually effective if the relative humidity is above 60 percent. However, certain materials such as
metallic powders and some pyrotechnic mixtures cannot be exposed to air with 60 percent
Figure 5-1. Testing shoes on wearer.
DOE-HDBK-1092-2004
5-5
relative humidity because of the possibility of their spontaneous ignition. Where this technique is
used to prevent accumulations of static electricity, a daily check of the humidity levels will be
performed before work starts.
5.1.4.7 GROUND-FAULT CIRCUIT INTERRUPTER
GFCI protection shall be provided in static-grounded areas where personnel are using hand-
held, portable, ac-powered electrical equipment operating at 120 V.
5.1.5 ELECTRICAL EQUIPMENT AND WIRING
Electrical equipment and wiring in locations containing explosives shall comply with relevant
provisions of the NEC and DOE regulations, plus the requirements in this section.
5.1.5.1 PERMANENT EQUIPMENT AND WIRING
The NEC and this section are minimum requirements for DOE facilities containing explosives.
Though the NEC does not specifically address explosives, Article 500, Hazardous (Classified)
Locations, does establish requirements for the design and installation of electrical equipment
and wiring in locations containing combustible dusts and flammable liquids, vapors, or gases
that in general are comparably hazardous. All permanent electrical equipment and wiring in
work areas containing explosives hazards shall conform to the standards of the NEC Hazardous
Locations Class II or Class I and II (dual rated). For Class II installations, provisions should be
made for easy conversion to Class I.
5.1.5.2 HAZARDOUS LOCATIONS
NEC definitions of and requirements for hazardous locations Class I and Class II are modified
as follows for application to DOE explosives facilities:
1. Areas containing explosive dusts or explosives which may, through handling or processing,
produce dust capable of being dispersed in the atmosphere shall be regarded as Class II
Division 1 hazardous locations.
2. Areas that contain exposed explosives but where no dust hazard exists shall be regarded as
Class 11 Division 2 hazardous locations.
3. Suitable National Electrical Manufacturers Association (NEMA)-rated enclosures shall be
provided in those locations where water/ explosives mixtures may contact electrical
equipment and wiring.
4. Areas where explosives are processed and sublimation may occur or where flammable
gases or vapor may be present in quantities sufficient to produce explosive or ignitable
mixtures shall be regarded as Class I Division 1 and Class II Division 1 hazardous locations.
Section 48
5. To ensure a location is assigned to the proper hazardous location class and division, it is
necessary to know the properties of the explosives involved there, including, at a minimum,
sensitivity to heat and spark and thermal stability. If the properties of an explosive area are
such that Class II Group G equipment provides inadequate surface temperature limits,
special protection shall be provided or the equipment excluded from the hazardous location.
This equipment shall not have a surface temperature exceeding the lowest onset of the
DOE-HDBK-1092-2004
5-6
exotherm of the explosive as determined by the differential thermal analysis test or the
differential scanning calorimetry test. When NEC Class I or II equipment is not available, the
substitute equipment shall be purged or sealed to prevent explosives contamination, shall
be determined intrinsically safe by facility management, or shall be administratively
controlled. If the equipment is purged, it shall be monitored for flow.
6. Areas that contain explosives that are not defined as hazardous locations (areas containing
no dust, vapor, gas hazards, or exposed explosives; for example, storage magazines), shall
be evaluated and documented by facility management to ensure that electrical ignition
sources are minimized or shall be regarded as NEC Class II.
7. Procedures shall be established by each DOE facility to control the use and modification of
electrical equipment in explosives areas and ensure that uniform standards are adhered to
throughout the facility.
5.1.5.3 ELECTRICAL SUPPLY SYSTEMS
There may be multiple hazards where explosives facilities are located near electrical supply
lines. To protect against these hazards, the NESC (ANSI/IEEE C2) and the following
requirements apply to all new construction or major modification and should be considered for
existing facilities:
1. Electric lines serving explosive facilities shall be installed underground from a point not less
than 50 feet from such facilities. This also applies to communications and instrumentation
lines and security alarm systems.
2. Electric service lines required to be close to an explosives facility shall be no closer to that
facility than the length of the lines between the poles or towers supporting the lines, unless
an effective means is provided to ensure that broken, energized lines cannot come into
contact with and present a hazard to the facility or its appurtenances.
3. Unmanned electrical substations shall be no closer to explosives facilities than public traffic
route distances.
4. Electric transmission lines (carrying 69 kV or more) and the tower or poles supporting them
shall be located not closer to explosives than:
a. Inhabited-building distance if the line in question is part of a system serving a large, offsite
area.
b. Public traffic route distance if loss of the line shall not create serious social or economic
hardships.
c. Underground utility separation distance criteria found in Table 5-1.
DOE-HDBK-1092-2004
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Table 5-1. Quantity-distance separation
for protection of underground service installationsa
Quantity of explosive
(maximum pounds) Distance, m (ft)
100 26 (80)
200 26 (80)
500 26 (80)
1,000 26 (80)
2,000 26 (80)
5,000 26 (80)
10,000 26 (80)
20,000 28 (85)
50,000 36 (110)
100,000 46 (140)
250,000 62 (190)
a
If the planned building is designed to contain the
effects of an explosion, the formula D (distance) =
3.0 w1/3 (w=weight) can be used to determine
separation distances for less than 20,000 lb.
Section 49
5.1.5.4 BUILDING SERVICE ENTRANCE
The electrical service entrance for explosives facilities shall be provided with:
1. An intermediate, metal-oxide surge lightning arrester on the primary side of the transformer.
2. Surge arresters and surge capacitors on the supply side of the main service disconnect.
3. Interconnected grounding between the lightning arrester, surge arrester, surge capacitors,
service entrance ground, and building ground.
5.1.6 TESTING
Certain provisions shall be complied with before tests are performed. Qualified personnel shall
be used to determine the time and procedure of the test.
DOE-HDBK-1092-2004
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5.1.6.1 TEST SETUP
In setting up a test at a firing site, all preparatory work shall be completed before explosives are
received. Such work shall include the following items:
1. Checking all firing site safety devices at regular intervals. Such safety devices include
warning lights, door and gate firing circuit interlocks, emergency firing circuit cutoff switches,
and grounding devices (including those that are remote from the firing bunker).
2. Completing all firing pad and shot stand setup work that requires power tools or other
potential spark-producing devices. The firing pad shall be cleared of all unnecessary gear.
Special precautions and procedures shall be developed and implemented if power tools or
other spark-producing devices are needed after the explosive has been received at the firing
pad.
3. If a special structure is required, as much work as possible shall be accomplished on it,
including assembly of all materials.
4. When possible, all diagnostic equipment shall be set up and checked, and dry runs shall be
performed.
5.1.6.2 PIN SWITCHES AND OTHER NONINITIATING CIRCUITS
Whenever pin switches and other noninitiating circuits are to be checked (such as for charging
current or leakage) and are in contact with or close to explosives, the check shall be performed
remotely. Other noninitiating electrical circuits include strain gauges, pressure transducers, and
thermocouples, which may be affixed to or close to the explosives within an assembly. If a
continuity-only (resistance) check is desired, this may be accomplished as a contact operation
with an electrical instrument approved for use with the particular explosive device. When low-
firing current actuators are involved, it may be advisable to conduct these tests remotely.
5.1.6.3 LIGHTNING STORMS
All operations in open test-firing areas shall be discontinued during lightning storms when
explosives are present. Completion of a test after receipt of a lightning alert should be allowed
only if test preparation has progressed to the extent that discontinuance of testing would
represent a greater personnel risk than would completion of testing.
5.1.6.4 LOW-ENERGY ELECTROEXPLOSIVE DEVICES
When using hot-wire or low-energy EEDs for a test firing, the following requirements shall be
applied:
1. Establishment of procedures to ensure that RF, FM, and TV transmitters having
sufficient output energy to initiate an EED at the test site are either restricted to a safe
distance from the site or not operated. Tables 5-2, 5-3, and 5-4 specify minimum safe
distances for the various types of transmitters at several output power levels.
2. Blasting caps and other low-firing current igniters or detonators shall be kept separate
from explosives at all times, except during actual test charge assembly and setup.
DOE-HDBK-1092-2004
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Section 50
Table 5-2. Minimum safe distances between
radio frequency (RF) transmitters and electric blasting operations.
Minimum Safe Distances (ft) Transmitter power
(watts) Commercial AM broadcast
transmitters
HF transmitters other
than AM
100 750 750
500 750 1,700
1,000 750 2,400
4,000 750 4,800
5,000 850 5,500
10,000 1,300 7,600
25,000 2,000 12,000
50,000b
2,800 17,000
100,000 3,900 24,000
500,000,c 8,800 55,000
b Present maximum power of U.S. broadcast transmitters in commercial AM broadcast frequency
range (0.535 to 1.605 MHz).
c Present maximum for international broadcast.
Table 5-3. Minimum safe distances between TV and FM broadcasting
transmitters and electric blasting operations.,
Minimum safe distances (ft)
Effective radiation
power (watts)
Channels
2-6 & FM
Channels
7-13 UHF
Up to 1,000 1,000 750 600
10,000 1,800 1,300 600
100,000 b
3,200 2,300 1,100
316,000 c 4,300 3,000 1,450
1,000,000 5,800 4,000 2,000
5,000,000 d 9,000 6,200 3,500
10,000,000 10,200 7,400 6,000
100,000,000 - - -
b Present maximum power, channels 2 to 6 and FM.
c Present maximum power, channels 7 to 13.
d Present maximum power, channels 14 to 83.
DOE-HDBK-1092-2004
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Table 5-4. Minimum safe distances between
mobile RF transmitters and electric blasting operations.
Minimum safe distances (ft)
Transmitter power
(watts) MF b HF b VHF(1) b VHF(2) b, c UHF b
5 c - - - - -
10 40 100 40 15 10
50 90 220 90 35 20
100 125 310 130 50 30
180 d - - - 65 40
250 200 490 205 75 45
500 e - - 209 - -
600 f 300 760 315 115 70
1,000 g 400 980 410 150 90
10,000 h 1,200 - 1,300 - -
b MF 1.6 to 3.4 MHz Industrial
HF 28 to 29.7 MHz Amateur
VHF(1) 35 to 44 MHz Public use
50 to 54 MHz Amateur
VHF(2) 144 to 148 MHz Amateur
150.8 to 161.6 MHz Public use
UHF 450 to 460 MHz Public use
c Citizens band radio (walkie-talkie), 26.96 to 27.23 MHz and cellular telephones, 3 watts power, 845
MHz; minimum safe distance; 5 ft.
d Maximum power for 2-way mobile units in VHF, 15.08- to 161.6-MHz range, and for 2-way mobile and
fixed station units in UHF, 450- to 460-MHz range.
e Maximum power for major VHF 2-way mobile and fixed-station units in 35- to 44-MHz range.
f Maximum power for 2-way fixed-station units in VHF, 150.8- to 161.6-MHz range.
g Maximum power for amateur radio mobile units.
h Maximum power for some base stations in 42- to 44-MHz band, 1.6- to 1.8- MHz band.
3. The entire wiring system of the explosive charge and of any low-firing-current initiators shall be
kept insulated at all times from every possible source of extraneous current. Shunts shall be left
on all low-energy initiators or lead wires until actual connections are to be made. Connections
shall be taped or otherwise insulated.
4. Test unit low-firing-current actuators or detonators shall be clearly marked. No contact
operations involving electrical testing shall be permitted on this type of unit unless an electric
meter for the specific application is used.
DOE-HDBK-1092-2004
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5.1.6.5 WARNING SIGNALS
Each DOE explosives testing facility shall use standard audible signals to warn personnel of any
impending firing in a test area. Signals shall be established by each facility and approved by facility
management.
5.1.6.6 FIRING LEADS
All detonator lead wires shall be electrically insulated. Firing leads or cables of low-energy
detonators for explosive assemblies shall be kept properly shorted during setup on the firing
point.
5.1.6.7 ELECTRICAL TESTING INSTRUMENTS FOR USE WITH EXPLOSIVES SYSTEMS
Section 51
Testing instruments shall meet certain criteria and be certified and labeled for the types of
testing they are permitted to perform.
5.1.6.7.1 CLASSIFICATION
Testing instruments shall be assigned to categories on the basis of electrical characteristics that
affect their safe use with explosives systems. Specifically, instrument categories shall be
established so that testing instruments in each category can be safely applied to one or more of
the following classes of explosives systems:
1. Low-energy or hot-wire initiators (blasting caps, actuators, squibs, etc.)
2. High-energy initiators (exploding bridgewires, slappers, etc.)
3. Noninitiating electrical circuits.
Testing instruments that do not meet the safety criteria may be used on an explosives system
only if the activity is considered a remote operation and adequate personnel shielding or
separation distance is provided.
5.1.6.7.2 CERTIFICATION
Each DOE facility using electrical testing instruments on explosives systems shall establish a
formal system for reviewing and certifying those instruments. Procedures for marking
instruments to show their approved use and restrictions on their use shall also be established,
so that every testing instrument is prominently labeled with its approved use and with a warning
if there is a restriction on its use.
Inspection and calibration of certified instruments shall be required at prescribed intervals or
whenever the instrument is opened for servicing or repair.
Records of all certified testing instruments shall be maintained by each DOE facility using
electrical instruments to test explosives systems. These records shall include type,
manufacturer, model, electrical specifications, wiring diagrams, and failure mode analyses. The
Explosives Safety Committee chairperson shall be notified in writing by DOE facilities when they
approve new electrical testing instruments for use with initiating systems. The chairperson shall
disseminate this information to all committee members.
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5.1.6.7.3 ELECTRICAL TESTING INSTRUMENTS FOR USE WITH INITIATING
ELECTRICAL CIRCUITS
Instruments used with electrical initiating circuits connected to electro-explosive devices may be
further categorized for use with either low-energy initiators or high-energy initiators. All testing
instruments used for this purpose shall be current-limited. Before being used on initiating
circuits, every instrument wiring diagram and internal circuitry design shall be analyzed,
examined, and certified for the following:
1. The output current through a resistance equivalent to that of the minimum resistance
initiator of the class shall not exceed 1 percent and shall not exceed 10 percent of the no-
fire rating for the most sensitive initiator of the class. The current-limiting features of the
testing instrument shall be internal to the instrument and shall not depend on the circuit load
characteristics.
2. The internal circuitry shall ensure isolation features that require, at a minimum, two
independent failure modes before the specified output current can be exceeded.
3. A comprehensive (point-to-point, if possible) wiring check shall be made to ensure that the
wiring corresponds to the diagram and that all components are functioning properly and
within specifications.
5.1.6.7.4 ELECTRICAL TESTING INSTRUMENTS FOR USE WITH NONINITIATING
ELECTRICAL CIRCUITS
Section 52
Testing instruments in this category are used with electric circuits connected to instruments
such as strain gauges, pin switches, pressure transducers, thermocouples, and electrical
components that are affixed to or within an assembly with explosives. These instruments shall
meet the following requirements:
1. Each use of the testing instrument shall be analyzed to ensure that there is no credible
scenario where the normal test energy from the testing instrument can ignite explosive
charges or initiators in the test. This testing shall be consistent with Section 5.1.6.7.3.
2. Where a testing instrument is used to make measurements on sensors directly applied to
explosives (e.g., bonded strain gauges or pin switches), the testing instrument shall be
certified and controlled.
3. Testing instruments shall be prominently marked with restrictions on their use. Many of
these testing instruments do not meet the requirements for use with initiating systems and
shall be marked to prevent their use on this type of circuit.
5.2 PREVENTION OF EXTERNAL IGNITION AND EXPLOSION
Explosives are hazardous by themselves, but around electricity they become even more
dangerous: an arc, spark, or hot surface can easily touch off an explosion. Therefore, the
electrical installation shall contain these ignition sources or house them in an area well
separated from the explosives storage area.
The electrical installation shall prevent accidental ignition of flammable liquids, vapors, and
dusts in the atmosphere. In addition, because portable electrical equipment is often used
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outdoors or in corrosive atmospheres, its material and finish should be such that maintenance
costs and shutdowns are minimized. (See Figure 5-2.)
5.2.1 SOURCES OF IGNITION
When flammable gases or combustible dusts are mixed in the proper proportion with air, a
source of energy is all that is needed to touch off an explosion. One prime source of energy is
electricity. During normal operation, equipment such as switches, circuit breakers, motor
starters, pushbutton stations or plugs, and receptacles can produce arcs or sparks when
contacts are opened and closed, which can easily cause ignition. Other energy hazards are
devices that produce heat, such as lighting fixtures and motors. Surface temperatures of these
devices may exceed the safe limits of many flammable atmospheres. Finally, many parts of the
electrical system can become potential sources of ignition in the event of insulation failure.
Included in this category are wiring (particularly splices), transformers, impedance coils,
solenoids, and other low-temperature devices without make-or-break contacts.
Nonelectrical sources such as sparks from metal can also easily cause ignition: a hammer, file,
or other tool dropped on masonry or on a nonferrous surface could be a hazard unless it is
made of nonsparking material. For this reason, portable electrical equipment is usually made
from aluminum or other material that will not produce sparks if it is dropped.
Figure 5-2. Arcs and sparks are sources of ignition that produce enough heat to cause
an explosion if the air and gas mixture is between the lower and upper flammable
limits of the liquid involved.
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5.2.2 COMBUSTION PRINCIPLES
The following three basic conditions are necessary for a fire or explosion to occur:
1. A flammable liquid, vapor, or combustible dust is present in sufficient quantity.
Section 53
2. A flammable liquid, vapor, or combustible dust mixes with air or oxygen in the proportion
required to produce an explosive mixture.
3. A source of energy is applied to the explosive mixture.
In applying these principles, the quantity of the flammable liquid or vapor that may be liberated
and its physical characteristics are taken into account. Also, vapors from flammable liquids have
a natural tendency to disperse into the atmosphere and rapidly become diluted to
concentrations below the lower explosion limit, particularly when there is natural or mechanical
ventilation. Finally, the possibility that the gas concentration may be above the upper explosion
limit does not ensure any degree of safety since the concentration first passes through the
explosive range to reach the upper explosion limit.
5.2.3 EVALUATION OF HAZARDOUS AREAS
Each area that contains gases or dusts that are considered hazardous shall be carefully
evaluated to make certain that the correct electrical equipment is selected. Many hazardous
atmospheres are Class I Group D or Class II Group G. However, certain areas may involve
other groups, particularly Class I Groups B and C. Conformity with the NEC requires the use of
fittings and enclosures approved for the specific hazardous gas or dust involved. The
determination of the area classification wiring and equipment selection for Class I, II, and III
areas should be made by a person cognizant of the requirements. The determination of the area
classification, wiring, and equipment selection for Class I, Zone 0, 1, and 2 areas shall be under
the supervision of a qualified registered professional engineer.
5.2.4 INTRINSICALLY SAFE EQUIPMENT
The use of intrinsically safe equipment is primarily limited to process control instrumentation
because these electrical systems lend themselves to the low energy requirements. The
installation rules are covered in Article 504 of the NEC. The definition of intrinsically safe
equipment and wiring is: "Equipment and wiring that are incapable of releasing sufficient
electrical energy under normal or abnormal conditions to cause ignition of a specific hazardous
atmospheric mixture in its most easily ignited concentration." UL and Factory Mutual list several
devices in this category. The equipment and its associated wiring shall be installed so they are
positively separated from the nonintrinsically safe circuits. Induced voltages could defeat the
concept of intrinsically safe circuits.
5.2.5 ENCLOSURES
In Class I Division 1 and 2 locations, conventional relays, contactors, and switches that have
arcing contacts shall be enclosed in explosion-proof housings, except for those few cases
where general-purpose enclosures are permitted by the NEC. By definition, enclosures for these
locations must prevent the ignition of an explosive gas or vapor that may surround it. In other
words, an explosion inside the enclosure shall not start a larger explosion outside. Adequate
strength is one requirement for such an enclosure. For an explosion-proof enclosure, a safety
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factor of 4 is used. That is, the enclosure shall withstand a hydrostatic pressure test of four
times the maximum pressure from an explosion within it.
Section 54
In addition to being strong, the enclosure shall be flame-tight. This term does not imply that the
enclosure is hermetically sealed but rather that the joints cool the hot gases resulting from an
internal explosion so that by the time they reach the outside hazardous atmosphere, they are
too cool to affect ignition. The strains and stresses caused by internal explosive pressures are
illustrated in Figure 5-3 (dotted lines indicate the shape that a rectangular enclosure strives to
attain under these conditions). Openings in an enclosure strive to maintain the shape of the
enclosure. Openings in an explosion-proof enclosure can be threaded-joint type (Figure 5-4) or
flat-joint type (Figure 5-5).
Figure 5-3. The right mixture of air and gases in an enclosure can cause an explosion
that creates internal pressures that can rupture the enclosure if not released properly.
Figure 5-4. Threaded joints can be used as an escape path to cool the hot gases as
they pass through the threads to the outside of the enclosure.
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In Class II locations, the enclosure shall keep dust out of the interior and operate at a safe
surface temperature. Because there will be no internal explosions, the enclosure may have
thinner wall sections. The construction of these enclosures is known as dust-ignition-proof.
5.2.6 PURGING/PRESSURIZATION SYSTEMS
Purging/pressurization systems permit the safe operation of electrical equipment under
conditions of hazard for which approved equipment may not be commercially available. For
instance, most switchgear units and many large motors do not come in designs listed for Class I
Groups A and B. Whether cast-metal enclosures or sheet-metal enclosures with pressurization
should be used for hazardous locations is mainly a question of economics, if both types are
available. As a typical example, if an installation had many electronic instruments that could be
enclosed in a single sheet-metal enclosure, the installation lends itself to the
purging/pressurization system. However, if the electronic instruments require installation in
separate enclosures, use of the cast metal in hazardous-location housing would almost
invariably prove more economical. Pressurized enclosures require:
1. A source of clean air or inert gas
2. A compressor to maintain the required pressure on the system
3. Pressure control valves to prevent the power from being applied before the enclosures have
been purged and to deenergize the system should pressure fall below a safe value.
Figure 5-5. Flat (ground) joints can be used as an escape path to cool the hot gases as
they pass through the flat (ground) joint.
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In addition, door-interlock switches are required to prevent access to the equipment while the
circuits are energized. All of these accessories can add up to a considerable expenditure. For a
detailed description of purging/pressurizing systems see NFPA 496, Purged and Pressurized
Enclosures for Electrical Equipment in Hazardous Classified Locations.
5.3 HAZARDOUS LOCATIONS
Hazardous areas and locations are classified by group, class, and division. These classifications
are determined by the atmospheric mixtures of various gases, vapors, dust, and other materials
present. The intensity of the explosion that can occur depends on concentrations, temperatures,
and many other factors that are listed in NFPA codes.
Section 55
Hazardous locations must be well understood by anyone designing, installing, working on, or
inspecting electrical equipment and wiring in such areas. Such locations carry a threat of
flammable or combustible gases, vapors, or dusts being present some or all of the time.
Information in this section will assist in classifying areas or locations with respect to hazardous
conditions, whether from atmospheric concentrations of hazardous gases, vapors, and deposits,
or from accumulations of readily ignitable materials.
This section covers the requirements for electrical equipment and wiring in locations that are
classified according to the properties of the flammable vapors, liquids, or gases or combustible
dusts that may be present and the likelihood that a flammable or combustible concentration is
present. The hazardous (classified) locations are assigned the following designations:
1. Class I Division 1
2. Class I Division 2
3. Class II Division 1
4. Class II Division 2.
5. Class I, Zone 0, Zone 1, Zone 2
Class III fibers and flyings are not covered in this section:
5.3.1 CLASS I
Class I locations are identified in the NEC as those in which flammable gases or vapors are or
may be present in the air in amounts sufficient to create explosive or ignitable mixtures. Gases
or vapors may be continuously or intermittently present. However, if a gas or vapor is present,
there is a potential that a flammable mixture will be present.
From an engineering standpoint, greater precautions are needed if a particular set of conditions
is likely to occur (e.g., the presence of a flammable mixture within the explosive range) than if it
is unlikely. This is the reason for dividing hazardous locations into two divisions.
5.3.1.1 DIVISION 1
NEC 500.5 defines Class I Division 1 hazardous locations as those in which:
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1. Ignitable concentrations of flammable gases, liquids, or vapors can exist under normal
operating conditions;
2. Ignitable concentrations of such gases or vapors may exist frequently because of repair or
maintenance operations or because of leakage; or
3. Breakdown or faulty operation of equipment or processes might release ignitable
concentrations of flammable gases, liquids, or vapors and might also cause simultaneous
failure of electrical equipment.
Note: In each case, ignitable concentrations are mentioned. This means concentrations
between the lower and upper flammable or explosion limits (see Section 5.3.5 and Table 5-5).
The fine-print note to NEC 500.5(B)(1) describes a number of areas and occupancies normally
classified as Class I Division 1 locations.
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Table 5-5. Class I Division 1 and Class I Division 2 summary of selected hazardous atmospheres
Group3 Atmosphere °F Ignition1
Temp.°C
Ignition2
energy
(millijoules)
Flammable limits3
(% by volume)
Lower Upper
Flashpoint3
°F °C
NEMA enclosure4
classification
Indoor Outdoor
A Acetylene 581 305 0.017 2.5 100.0 Gas Gas 7 8
B 1,3-butadiene 788 420 - 2.0 12.0 Gas Gas 7 8
B Ethylene oxide 804 429 - 3.0 100.0 -20 -28 7 8
B Hydrogen 968 520 0.017 4.0 75.0 Gas Gas 7 8
B Manufactured gas containing more
than 30% hydrogen by volume - - - - - - - - -
B Propylene oxide 840 449 - 2.6 36.0 -35 -37 7 8
C Acetaldehyde 347 175 - 4.0 60.0 -38 -39 7 9
C Diethyl ether 320 160 - 1.9 36.0 -49 -45 7 8
C Ethylene 842 450 0.08 2.7 36.0 Gas Gas 7 8
C Unsymmetrical dimethyl hydrazine
(UDMH) 480 249 - 2.0 95.0 5 -15 7 8
Section 56
D Acetone 869 465 - 2.5 13.0 -4 -20 7 8
D Acrylonitrile 898 481 - 3.0 17.0 32 0 7 8
D Ammonia 928 498 - 15.0 28.0 Gas Gas 7 8
D Benzene 928 498 - 1.3 7.9 12 -11 7 8
D Butane 550 288 - 1.6 8.4 Gas Gas 7
D 1-butanol 650 343 - 1.4 11.2 98 37 7 8
D 2-butanol 761 405 - 1.7@212°F 9.0@212°F 75 24 7 8
D n-butyl acetate 790 421 - 1.7 7.6 72 22 7 8
D Cyclopropane 938 503 0.25 2.4 10.4 Gas Gas 7 8
D Ethane 882 472 - 3.0 12.5 Gas Gas 7 8
D Ethanol 685 363 - 3.3 19.0 55 13 7 8
D Ethylacetate 800 427 - 2.0 11.5 24 -4 7 8
D Ethylene dichloride 775 413 - 6.2 16.0 56 13 7 8
D Gasoline 536 to 880 280 to 471 - 1.2 to 1.5 7.1 to 7 7 8 7 8
D Heptane 399 204 - 1.05 6.7 -36 to -50 -38 to -46 7 8
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Table 5-5. Class I Division 1 and Class I Division 2 summary of selected hazardous atmospheres (continued).
Group3 Atmosphere °F Ignition1
Temp.°C
Ignition2
energy
(millijoules)
Flammable limits3
(% by volume)
Lower Upper
Flashpoint3
°F °C
NEMA enclosure4
classification
Indoor Outdoor
D Hexane 437 225 - 1.1 7.5 -7 -22 7 8
D Isoamyl alcohol 662 350 - 1.2 9.0@212°F 109 43 7 8
D Isoprene 428 220 - 1.5 8.9 -65 -54 7 8
D Methane 999 630 0.30 5.0 15.0 Gas Gas 7 8
D Methanol 725 385 - 6.0 36.0 52 11 7 8
D Methyl ethyl ketone 759 404 - 1.7@200°F 11.4@200°F 16 -9 7 8
D Methyl isobutyl ketone 840 449 - 1.2@200°F 8.0@200°F 64 18 7 8
D 2-methyl-l-propanol 780 416 - 1.7@123°F 10.6@202°F 82 28 7 8
D 2-methyl-2-propanol 892 478 - 2.4 8.0 52 11 7 8
D Naphtha (petroleum) 550 288 - 1.1 5.9 <0 <-18 7 8
D Octane 403 206 - 1.0 6.5 56 13 7 8
D Pentane 470 243 - 1.5 7.8 < -40 < -40 7 8
D 1-pentanol 572 300 - 1.2 10.0@212°F 91 33 7 8
D Propane 842 450 0.25 2.1 9.5 Gas Gas 7 8
D 1-propanol 775 413 - 2.2 13.7 74 23 7 8
D 2-propanol 750 399 - 2.0 12.7@200°F 54 12 7 8
D Propylene 851 455 - 2.0 11.1 Gas Gas 7 8
D Styrene 914 490 - 1.1 7.0 88 31 7 8
D Toluene 896 480 - 1.2 7.1 40 4 7 8
D Vinyl acetate 756 402 - 2.6 13.4 18 -8 7 8
D Vinyl chloride 882 472 - 3.6 33.0 Gas Gas 7 8
D Xylenes 867 to 984 464 to 529 - 1.0 to 1.1 7.6 81 to 90 27 to 32 7 8
Notes:
1 See NFPA 325 and 497M.
2 See "Handbook of Fire Protection Engineering", Society of Fire Protection Engineers.
3 See NFPA 325.
4 See NEMA 250, "Enclosures for Electrical Equipment."
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NEC Article 100 defines a flammable liquid as one that has a flashpoint below 38°C (100°F) or
one whose temperature is raised above its flashpoint. Flashpoint is the lowest temperature to
which a combustible or flammable liquid may be heated before sufficient vapors are driven off
and the liquid will flash when brought into contact with a flame, arc, spark, or another ignition
source. (See Section 1-3 of NFPA 497M for more details.)
5.3.1.2 DIVISION 2
NEC 500.5(B)(2) defines Class I Division 2 locations as those:
1. In which flammable liquids or gases are handled, processed, or used, but where such
materials are normally confined in closed containers or closed systems from which they can
escape only in case of accidental rupture or breakdown of such containers or systems or in
case of abnormal equipment operation.
2. In which gases or vapors are normally prevented, by positive mechanical ventilation, from
forming ignitable concentrations and which might become hazardous through failure or
abnormal operation of the ventilating equipment
3. That are adjacent to a Class I Division 1 location and to which ignitable concentrations of
gases or vapors might occasionally be transmitted unless such transmittal is prevented by
adequate positive-pressure ventilation from a source of clean air, and effective safeguards
against ventilation failure are provided.
The fine-print note #2 to NEC 500.5 describes a number of areas and occupancies normally
classified as Class I Division 2 locations. For example, piping systems without valves, meters,
and devices do not usually cause a hazardous condition, even though they carry flammable
liquids, because they are considered a contained system. Therefore, the surro