(1) In every completely insulated feeder circuit in excess of 25 kilowatts capacity, leading underground and operating at a potential not exceeding the limits of medium voltage, there shall be provided above ground a circuit breaker arranged to open simultaneously each ungrounded conductor. In addition, a positive disconnect means shall be installed outby the circuit breaker. Overload protection shall be provided to open the circuit breaker in case of overload on any conductor. Fuses may be substituted for circuit breakers in circuits transmitting 25 kilowatts or less. Each power circuit in excess of 50 kilowatts leading underground shall be provided with a suitable ammeter.

(2) Every alternating current feeder circuit leading underground and operating at a potential exceeding the limits of medium voltage shall be provided above ground with a suitable circuit breaker. The breaker shall be equipped with automatic overload trip, arranged to open simultaneously each ungrounded power-carrying conductor. Each circuit shall also be provided with a suitable ammeter.

(1) All cables passing underground through inclines, boreholes and shafts shall be installed in a manner that will prevent undue strain in the sheath, insulation or conductors and damage by chafing of cables against each other or against the borehole casing or shaft. All ungrounded power conductors in shafts, boreholes and inclines shall be covered with suitable insulating materials and installed to provide a minimum tensile factor of safety of five. Conductors shall be securely fastened and properly supported out of contact with combustible materials. When the weight, length and construction of a cable are such that suspension from its upper end only would subject the cable to possible damage, it shall be supported at intervals necessary to prevent undue strains in the sheath, insulation and conductors and to provide a minimum tensile factor of safety of five. Adequate protection shall be provided so that no damage can result from water, electrolysis, moving cages, skips, ice, coal or other falling or moving materials.

(2) Installation of direct current and alternating current cables carrying in excess of 25 kilowatts in the same borehole shall require approval of the department.

(1) No power wires or cables having what is commonly termed as weatherproof insulation or insulation consisting of braided covering, which is susceptible to moisture absorption from the outer surface to the conductor, shall be installed in a mine.

(2) All insulated power cables purchased for use in a mine shall be protected by a flame-resistant jacket and assigned an approval number unless either armored or installed in rigid steel conduit, a metal enclosure or a fireproof room.

(1) Bare power conductors shall not be installed in an air current that has passed through or by the first working place in the air split.

(2) High-voltage transmission cable, high-voltage motors and high-voltage transformers shall not be installed in any air current that has passed through or by the first working place in the air split.

(1) Where the cables or feed wires, other than trolley wires, in main haulage roads cannot be kept at least 12 inches from any part of a mine car or locomotive, they shall be specially protected by proper guards.

(2) Cables and wires, except trailing or portable cables or bare return cables, shall be installed on roofs, ribs, walls or timbers by means of efficient insulators. All electric cables constantly kept in rooms or pillars or other work areas shall be carried on suitable supports to within 70 feet of the face of each work area. In no instance shall the method of support damage the cable jacket or armor.

(3) When main or other roads are being repaired or blasting is being carried on, suitable temporary protection from damage shall be given to the cables.

(4) All other wires, except telephone, shot-firing and signal wires, shall be on the same side of the road as the trolley wire.

(5) Haulage block signal circuits and other control circuits powered from the trolley shall be located on the same side of the road as the trolley.

(1) Any motor-generator, rectifier except those described in subsection (r), rotary converter or oil-filled transformer installed in a mine shall be enclosed in a fireproof chamber of masonry or in an effectively grounded approved steel structure. These buildings shall be provided with automatically closing fire doors, but the automatic features of fire doors may be omitted if a substation attendant is employed. The openings of the doors shall be safeguarded by grillwork so that only authorized individuals may enter the room. No electrical equipment containing inflammable material shall be placed within eight feet of a door or opening in the underground building. All underground substations containing rotary machinery shall have an attendant constantly on duty while rotating machinery is in operation, unless adequate control and protection of the equipment is assured by the use of suitable automatic devices. No transformer, circuit breaker, controller or other device containing more than 20 gallons of inflammable liquid shall be placed in any underground substation. A separate split of air shall adequately ventilate the substation. No substation shall be built in any mine until the location, material, construction and method of ventilation for the substation has received the approval of the department.

(2) Main and distribution switch and fuse boards shall be made of incombustible, moisture-resistant, insulating material and fixed in as dry a situation as practicable or shall be of suitable metal construction, exposed portions of which shall be effectively grounded. All switches, circuit breakers, rheostats, fuses and instruments used in connection with underground motor-generators, rotary-converters, high-voltage motors, transformers and low-voltage and medium-voltage motors of more than 50 horsepower or 50 KVA capacity shall be installed upon a suitable switchboard or in a metal-clad switchgear structure. Similar equipment for low-voltage and medium-voltage motors of 50 horsepower and less may be separately installed if mounted upon insulating bases of suitable material or effectively metal clad.

(1) In underground stations where switchboards are installed, there shall be a passageway in front of the switchboard not less than three feet in width, and, if there are any high-voltage connections at the back of the switchboard, any passageway behind the switchboard shall not be less than three feet. The floor at the back of the switchboard shall be properly floored and insulated with nonconducting material, accessible from each end. In the case of high-voltage, switchboards shall be kept locked, but the lock shall allow the door being opened from the inside without the use of a key.

(2) Where the supply is at a voltage exceeding the limits of medium voltage, there shall be no live metal work on the front of the main switchboard within seven feet of the floor or platform, and the space provided under paragraph (1) shall not be less than four feet. Insulating floors or mats shall be provided for medium-voltage boards where live metal work is on the front.