Health, Safety & Environment ยป Health, Safety & Environment Manual

Section 16 - Electrical Safety

SCOPE

To provide a general overview of electrical safety.  Not all acceptable safety measures are contained in this procedure.  Additional measures required under exceptional conditions or circumstances may be obtained from the National Electric Codes (NEC).

 

General Electrical Guidelines

  1. Electrical equipment shall be free from recognized hazards that are likely to cause death or serious physical harm to employees.  Safety of equipment shall be determined using the following considerations:
    1. Listed or labeled equipment shall be used or installed in accordance with any instructions included in the listing or labeling.
    2. Conductors shall be spliced or joined with splicing devices suitable for the use or by brazing, welding, or soldering with a fusible metal or alloy.
    3. All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an insulating device suitable for the purpose.
    4. Parts of electric equipment which in ordinary operation produce arcs, sparks, flames, or molten metal shall be enclosed or separated and isolated from all combustible material.
  2. Electrical equipment may not be used unless the manufacturer's name, trademark, or other descriptive marking by which the organization responsible for the product may be identified is placed on the equipment.  Other markings shall be provided giving voltage, current, wattage, or other ratings as necessary.  The marking shall be of sufficient durability to withstand the environment involved.
  3. Each disconnecting means for motors and appliances shall be legibly marked to indicate its purpose, unless located and arranged so the purpose is evident.
  4. Each service, feeder, and branch circuit, at its disconnecting means or over-correct device, shall be legibly marked to indicate its purpose, unless located and arranged so the purpose is evident.

600 VOLTS, NOMINAL, OR LESS

  1. Sufficient access and working space shall be provided and maintained about all electric equipment to permit ready and safe operation and maintenance of such equipment.
  2. The dimension of the working space in the direction of access to live parts operating at 600 volts or less and likely to require examination, adjustment, servicing, or maintenance while alive may not be less than indicated in Table S-1.  In addition to the dimensions shown in Table S-1, workspace may not be less than 30 inches wide in front of the electric equipment.  Distances shall be measured from the live parts if they are exposed, or from the enclosure front or opening if the live parts are enclosed.  Concrete, brick, or tile walls are considered to be grounded. Working space is not required in back of assemblies such as dead-front switchboards or motor control centers where there are no renewable or adjustable parts such as fuses or switches on the back and where all connections are accessible from locations other than the back

                                                         TABLE S-1 - WORKING CLEARANCES 
                                     ____________________________________________ 
                                                Nominal voltage      |     Minimum clear distance 
                                                to ground                |     for condition (2)(ft)
                                             ________________  |________________________ 
                                                               |            | (a)      |  (b)    |  (c)
                                    _____________ |_____  |____   |_____ |_ 
                                        0-150 ...........  |  (1)3   |   (1)3  |    3     |
                                     151-600 .......  |  (1 3    | 3 1/2  |    4     | 
                                     _____________|______ |_____ |______|
    Footnotes
    1. Minimum clear distances may be 2 feet 6 inches for installations built prior to April 16, 1981.
    2. Conditions a, b, and c, are as follows:
      1. Exposed live parts on one side and no live or grounded parts on the other side of the working space, or exposed live parts on both sides effectively guarded by suitable wood or other insulating material.  Insulated wire or insulated busbars operating at not over 300 volts are not considered live parts.
      2. Exposed live parts on one side and grounded parts on the other side.
      3. Exposed live parts on both sides of the workspace [not guarded as provided in Condition (a)] with the operator between.
  3. Working space may not be used for storage.  When normally enclosed live parts are exposed for inspection or servicing, the working space, if in a passageway or general open space, shall be suitably guarded.
  4. At least one entrance of sufficient area shall be provided to give access to the working space about electric equipment.
  5. Where there are live parts normally exposed on the front of switchboards or motor control centers, the working space in front of such equipment may not be less than 3 feet.
  6. Illumination shall be provided for all working spaces about service equipment, switchboards, panel boards, and motor control centers installed indoors.
  7. The minimum headroom of working spaces about service equipment, switchboards, panel-boards, or motor control centers shall be 6 feet 3 inches.
    NOTE: As used in this section a motor control center is an assembly of one or more enclosed sections having a common power bus and principally containing motor control units.
  8. Except as required or permitted, live parts of electric equipment operating at 50 volts or more shall be guarded against accidental contact by approved cabinets or other forms of approved enclosures, or by any of the following means:
    1. By location in a room, vault, or similar enclosure that is accessible only to qualified persons.
    2. By suitable permanent, substantial partitions or screens so arranged that only qualified persons will have access to the space within reach of the live parts.  Any openings in such partitions or screens shall be so sized and located that persons are not likely to come into accidental contact with the live parts or to bring conducting objects into contact with them.
    3. By location on a suitable balcony, gallery, or platform so elevated and arranged as to exclude unqualified persons.
    4. By elevation of 8 feet or more above the floor or other working surface.
  9. In locations where electric equipment would be exposed to physical damage, enclosures or guards shall be so arranged and of such strength as to prevent such damage.
  10. Entrances to rooms and other guarded locations containing exposed live parts shall be marked with conspicuous warning signs forbidding unqualified persons to enter.

OVER 600 VOLTS, NOMINAL

  1. Enclosure for electrical installations.  Electrical installations in a vault, room, closet or in an area surrounded by a wall, screen, or fence, access to which is controlled by lock and key or other approved means, are considered to be accessible to qualified persons only. 
  2. A wall, screen, or fence less than 8 feet in height is not considered to prevent access unless it has other features that provide a degree of isolation equivalent to an 8 foot fence. 
  3. The entrances to all buildings, rooms, or enclosures containing exposed live parts or exposed conductors operating at over 600 volts, nominal, shall be kept locked or shall be under the observation of a qualified person at all times.
  4. Electrical installations having exposed live parts shall be accessible to qualified persons.
  5. Electrical installations that are open to unqualified persons shall be made with metal-enclosed equipment or shall be enclosed in a vault or in an area, access to which is controlled by a lock.
  6. If metal-enclosed equipment is installed so that the bottom of the enclosure is less than 8 feet above the floor, the door or cover shall be kept locked.
  7. Metal-enclosed switchgear, unit substations, transformers, pull boxes, connection boxes, and other similar associated equipment shall be marked with appropriate caution signs.  If equipment is exposed to physical damage from vehicular traffic, suitable guards shall be    provided to prevent such damage.
  8. Ventilating or similar openings in metal-enclosed equipment shall be designed so that foreign objects inserted through these openings will be deflected from energized parts.
  9. Sufficient space shall be provided and maintained about electric equipment to permit ready and safe operation and maintenance of such equipment.
  10. Where energized parts are exposed, the minimum clear workspace may not be less than 6 feet 6 inches high (measured vertically from the floor or platform), or less than 3 feet wide (measured parallel to the equipment).
  11. The depth shall be as required in Table S-2.  The workspace shall be adequate to permit at least a 90-degree opening of doors or hinged panels.
  12. The minimum clear working space in front of electric equipment such as switchboards, control panels, switches, circuit breakers, motor controllers, relays, and similar equipment may not be less than specified in Table S-2.
  13. Distances shall be measured from the live parts if they are exposed, or from the enclosure front or opening if the live parts are enclosed. 
  14. Working space is not required in back of equipment such as deadfront switchboards or control assemblies where there are no renewable or adjustable parts (such as fuses or switches) on the back and where all connections are accessible from locations other than the back.  Where rear access is required to work on deenergized parts on the back of enclosed equipment, a minimum working space of 30 inches horizontally shall be provided.
        
                                      TABLE S-2 - MINIMUM DEPTH OF CLEAR WORKING SPACE
                                                  IN FRONT OF ELECTRIC EQUIPMENT
                                 ____________________________________________________ 
                                                                               |   Conditions (2)(ft) 
                                 Nominal voltage to ground    |_______________________
                                                                               |           |
                                                                               |  (a)     |  (b)     |  (c)
                    _______________________             |_____ |_____ | _________________
                                   601 to 2,500 ..............    |    3     |    4     |    5 
                                2,501 to 9,000 .............     |    4     |    5     |    6
                                9,001 to 25,000 ............     |    5     |    6     |    9
                              25,001 to 75kV(1) ..........       |    6     |    8     |   10
                                Above 75kV(1) ..............     |    8     |   10    |   12 
                        ______________________            |_____ |_____ |__________________

    Footnotes
    1. Minimum depth of clear working space in front of electric equipment with a nominal voltage to ground above 25,000 volts may be the same as for 25,000 volts under Conditions (a), (b), and (c) for installations built prior to April 16, 1981.
    2. Conditions a, b, and c are as follows:
      1. (a) Exposed live parts on one side and no live or grounded parts on the other side of the working space, or exposed live parts on both sides effectively guarded by suitable wood or other insulating materials.  Insulated wire or insulated busbars operating at not over 300 volts are not considered live parts.
      2. (b) Exposed live parts on one side and grounded parts on the other side.  Concrete, brick, or tile walls will be considered as grounded surfaces.
      3. (c) Exposed live parts on both sides of the workspace not guarded as provided in Condition (a) with the operator between.
  15. Elevation of unguarded live parts. Unguarded live parts above working space shall be maintained at elevations not less than specified in Table S-3.

                           TABLE S-3 - ELEVATION OF UNGUARDED ENERGIZED PARTS
                                             ABOVE WORKING SPACE
    ______________________________________________________________________
                       Nominal voltage                 | 
                     between phases                  |    Minimum elevation
          ______________________ ___    |________________________________ 
                    601 to 7,500 ................  |    *8 feet 6 inches. 
                 7,501 to 35,000 ..............  |    9 feet.
    Over 35kV ................................ |    9 feet + 0.37 inches per kV above 35kV.
    _____________________________   |___________________________________
    Note: Minimum elevation may be 8 feet 0 inches for installations built prior to April 16,  1981 if the nominal voltage between phases is in the range of 601-6600 volts.
  16. At least one entrance not less than 24 inches wide and 6 feet 6 inches high shall be provided to give access to the working space about electric equipment.
  17. Switchboard and control panels exceeding 48 inches in width, there shall be one entrance at each end of such board where practicable.
  18. Where bare energized parts at any voltage or insulated energized parts above 600 volts are located adjacent to such entrance, they shall be suitably guarded.
  19. Permanent ladders or stairways shall be provided to give safe access to the working space around electric equipment installed on platforms, balconies, mezzanine floors, or in attic or roof rooms or spaces.
Section 16 - Electrical Safety
 


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16-1 Electrical Safety - General