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Subchapter 17. Mine Safety Orders
Article 47. Electrical Equipment and Practices

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§7183. Federal Electrical Standards.

(a) Except as provided herein, the Bureau of Mines Mandatory Electricity Standards published July 31, 1969, February 25, 1970 and December 8, 1970 are adopted as part of these orders and read as follows:

EXCEPTION: In no case shall the minimum requirements be less than those established in the Electrical Safety Orders, T-8, CAC and Part 3, T-24, CAC.


(1) (12-1) Circuits shall be protected against excessive overload by fuses or circuits breakers of the correct type and capacity.

(2) (12-2) Electric equipment and circuits shall be provided wit switches or other controls. Such switches or controls shall be of approved design and construction and shall be properly installed.

(3) (12-3) Individual overload protection and short circuit protection shall be provided for the trailing cables of mobile equipment.

(4) (12-7) Trailing cables and power-cable connections to junction boxes shall not be made or broken while energized.

(5) (12-11) High-potential transmission cables shall be covered, insulated, or placed to prevent contact with low-potential circuits.

(6) (12-14) Shovel trailing cables shall not be moved with the shovel dipper unless cable slings or sleds are used.

(7) (12-16) Electrical equipment shall be deenergized before work is done on such equipment. Switches shall be locked out or other measures taken which shall prevent the equipment from being energized without the knowledge of the individuals working on it. Such locks, or preventative devices shall be removed only by the persons who installed them or by authorized personnel.

(8) (12-17) Power circuits shall be deenergized before work is done on such circuits unless hotline tools are used. Suitable warning signs shall be posted by the individuals who are to do the work. Switches shall be locked out or other measures taken which shall prevent the power circuits from being energized without the knowledge of the individuals working on them. Such locks, signs, or preventative devices shall be removed only by the person who installed them or by authorized personnel.

(9) (12-18) All switches, automatic cutouts, or other control devices shall be located or marked as to clearly indicate the equipment controlled by them, and switches (excepting magnetic switches) shall indicate whether they are open or closed.

(10) (12-20) Dry wooden platforms, insulating mats, or other electrically-nonconductive material shall be kept in place at all switchboards and power-control switches where shock hazards exist. However, metal plates on which a person normally would stand and which are kept at the same potential as the grounded, metal, noncurrent-carrying parts of the power switches to be operated may be used.

(11) (12-21) Suitable danger signs shall be posted at all major electrical installations.

(12) (12-23) Electrical connections and resistor grids that are difficult or impractical to insulate shall be guarded, unless protection is provided by location.

(13) (12-25) All metal enclosing or encasing electrical circuits shall be grounded or provided with equivalent protection. This requirement does not apply to battery-operated equipment.

(14) (12-26) Metal fencing and metal buildings enclosing transformers and switchgear shall be grounded.

(15) (12-27) Frame grounding or equivalent protection shall be provided for mobile equipment powered through trailing cables.

(16) (12-28) Continuity and resistance of grounding systems shall be tested immediately after installation.

(17) (12-30) When a potentially dangerous condition is found it shall be corrected before equipment or wiring is energized.

(18) (12-33) Hand-held electric tools shall not be operated at high potential voltages.

(19) (12-36) Fuses shall not be removed or replaced by hand in an energized circuit, and they shall not otherwise be removed or replaced in an energized circuit unless equipment and techniques especially designed to prevent electric shock are provided and used for such purpose.

(20) (12-37) Fuse tongs or hot line tools shall be used when fuses are removed or replaced in high-potential circuits.

(21) (12-40) Operating controls shall be installed so that they can be operated without danger of contact with energized conductors.

(22) (12-41) Switches and starting boxes shall be of safe design and capacity.

(23) (12-45) Overhead high-potential powerlines lines shall be installed as specified by the Electrical Safety Orders and Part 3, T-24, CAC.

(24) (12-47) Guy wires of poles supporting high-potential conductors shall be equipped with insulators installed near the pole end.

(25) (12-48) Telegraph, telephone, or signal wires shall not be installed on the same crossarm with power conductors. When carried on poles supporting powerlines, they shall be installed as specified by the Electrical Safety Orders and Part 3, T-24, CAC.

(26) (4-10) Power wires and cables shall be adequately insulated. Flexible cords and cables shall not be used as a substitute for fixed wiring and shall be adequately protected when subject to physical damage.

(27) (4-11) Abandoned electrical circuits shall be de-energized and isolated so that they cannot become energized inadvertently.


(28) (12-65) Powerlines, including trolley wires, and telephone circuits shall be protected against short circuits and lightning.

(29) (12-66) Where metallic tools or equipment can come in contact with trolley wires or bare powerlines, the lines shall be guarded or deenergized.

(30) (12-67) Transformers shall be totally enclosed, located on poles or shall be enclosed in compliance with the Electrical Safety Orders.

(31) (12-68) Transformer enclosures shall be kept locked against unauthorized entry.

(32) Provisions for preventing accidents due to overhead high-voltage lines shall be in conformance with the High-Voltage Electrical Safety Orders, Article 86, which reads:

Article 86. Provisions for Preventing Accidents Due to Proximity of Overhead Lines

2946. Provisions for Preventing Accidents Due to Proximity to Overhead Lines.

(a) General. No person, firm, or corporation, or agent of same, shall require or permit any employee to perform any function in proximity to energize high-voltage lines; to enter upon any land, building, or other premises and thereto engage in any excavation, demolition, construction, repair, or other operation; or to erect, install, operate, or store in or upon such premises any tools, machinery, equipment, materials, or structures (including scaffolding, house moving, well drilling, pile driving, or hoisting equipment) unless and until danger from accidental contact with said high-voltage lines has been effectively guarded against.

(b) Clearances or Safeguards Required. Except where electrical distribution and transmission lines have been deenergized and visibly grounded or effective barriers have been erected to prevent physical and arcing contacts with the high-voltage lines, the following provisions shall be met:

(1) Over Lines. The operation, erection, or handling of tools, machinery, apparatus, supplies, or materials, or any part thereof, over energized high-voltage lines shall be prohibited.

(2) Equipment and Materials in Use. The operation, erection, or handling of tools, machinery equipment, apparatus, materials, or supplies, or any part thereof within the minimum clearances from energized lines set forth in Table X shall be prohibited.

                          Table X 
    Required Clearances from Overhead High-Voltage Lines 

              Nominal Voltage            Minimum Required     
              (Phase to Phase)           Clearance (Feet)       
           750- 50,000......................... 10 
        Over 50,000-75,000..................... 11 
        Over 75,000-125,000.................... 13 
  Over 125,000-175,000......................... 15 
  Over 175,000-250,000......................... 17 
  Over 250,000-370,000......................... 21 
  Over 370,000-550,000......................... 27 
  Over 550,000-1,000,000....................... 42 

(3) Transportation or Transit. The transportation or transit of any tool, machinery, equipment, or apparatus, or the moving of any house or other building in proximity to overhead high-voltage lines shall be expressly prohibited if at any time during such transportation or transit such tool, machinery, equipment, apparatus, or building or any part thereof, can come closer to high-voltage lines than the minimum clearances set forth in Table Y.

Except where the boom of boom-type equipment is lowered and no load is imposed thereon, the equipment in transit shall conform to the minimum required clearances set forth in Table X.

                            Table Y 

Required Clearances from Energized High-Voltage Conductors (While in Transit) 

            Nominal Voltage             Minimum Required
            (Phase to Phase)            Clearance (Feet)       
           750- 50,000.......................... 6 
  Over  50,000-345,000......................... 10 
  Over 345,000-750,000......................... 16 
  Over 750,000-1,000,000....................... 20 

(4) Storage. The storage of tools, machinery, equipment, supplies, materials, or apparatus under, by, or near energized high-voltage lines is hereby expressly prohibited if at any time during such handling or other manipulation it is possible to bring such tools, machinery, equipment, supplies, materials, or apparatus, or any part thereof, within the minimum required clearances from high-voltage lines as set forth in Table X.

(c) The specified clearance shall not be reduced by movement due to any strains impressed (by attachments or otherwise) upon the structures supporting the high-voltage line or upon any equipment, fixtures, or attachments thereon.

(d) Insulated cage-type boom guards, boom stops, insulating links, or proximity warning devices may be used on cranes, but the use of such devices shall not alter the required clearances set forth in Table X.

(e) Any overhead conductor shall be considered to be energized unless and until the person owning or operating such line verifies that the line is not energized, and the line is visibly grounded at the work site.

2947. Warning Signs Required. The owner, agent, or employer responsible for the operations of equipment shall post and maintain in plain view of the operator and driver on each crane, derrick, power shovel, drilling rig, hay loader, hay stacker, pile driver, or similar apparatus, a durable warning sign legible at 12 feet reading: "UNLAWFUL TO OPERATE THIS EQUIPMENT WITHIN 10 FEET OF HIGH-VOLTAGE LINES OF 50,000 VOLTS OR LESS."

In addition to the above wording, the following statement in small lettering shall be provided on the warning sign: "For Minimum Clearances Of High-Voltage Lines In Excess of 50,000 Volts. See Article 86, Title 8, High-Voltage Electrical Safety Orders."

2948. Notification to the Operators of High-Voltage Lines and

Responsibility for Safeguards.

When any operations are to be performed, tools, or materials handled, or equipment is to be moved or operated within the specified clearances of any energized high-voltage lines, the person or persons responsible for the work to be done shall promptly notify the operator of the high-voltage line of the work to be performed and shall be responsible for the completion of the safety measures as required by Order 2946(b) before proceeding with any work which would impair the aforesaid clearance.

2949. Special Exemptions.

The provisions of the foregoing Orders 2946 through 2948 shall not apply to the construction, reconstruction, maintenance, or operation of any energized high-voltage overhead lines or their supporting structure or appurtenances by qualified electrical workers, nor to work performed in proximity to high-voltage lines by qualified persons using approved equipment and work procedures.


(33) (12-80) Trolley wires and bare power conductors shall be guarded at man-trip loading and unloading points, and at shaft stations. Open unguarded trolley wires shall be placed not less than 9 feet above the track, or not less than 6 inches outside of the rail and not less than 7 feet above the rail.

(34) (12-82) Powerlines shall be well separated or insulated from waterlines, telephone lines, and air lines.

(35) (12-85) Transformer stations shall be enclosed to prevent persons from unintentionally or inadvertently contacting energized parts.

NOTE: Authority cited: Section 6500, Labor Code.


1. Repealer of subsection (a)(32) and new subsection (a)(32) filed 7-27-73, effective thirtieth day thereafter (Register 73, No. 30).

2. Editorial correction of subsection (a)(11) (Register 97, No. 25).

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