(a) High voltage cables leading underground and extending underground shall be of the multiple conductor flame resistant type with either a rubber, plastic or armor sheath meeting the requirements of the department for flame resistance. They shall be equipped with metallic shields around each power conductor. One or more ground conductors shall be provided of a total size either (1) not less than one-half the power conductor size, or (2) capable of carrying two times the maximum ground fault current. There shall also be provided an insulated conductor not smaller than No. 8 AGW for the ground-continuity check-circuit. Cables shall be adequate for the intended current and voltage. Splices made in the cable shall provide continuity of all components and shall be made in accordance with the cable manufacturers' recommendations. The making of such splices shall be supervised by a competent person designated by the mine electrician.

(b) High voltage cables subject to repeated flexing shall be similar in construction to type SHD-GC in accordance with Insulated Power Cable Engineers Association standard S-19-81.

(c) If couplers are used, they shall be of the three-phase type with a full metallic shell, and shall be adequate for the voltage and current expected. All exposed metal on the couplers shall be grounded to the ground conductor in the cable. The coupler shall be constructed so that the ground-continuity conductor shall be broken first and the ground conductor shall be broken last when the coupler is being uncoupled.

(d) Installations at locations where cables cross haulageways or travelways or where equipment must pass over or under cable, shall have the approval of the district mine inspector.

(e) High voltage cables shall be installed only in intake airways. They may be installed on intake haulageways only with written approval of the secretary. Such cable may be installed by hanging on suitable hooks or clamps, or by supporting by a suitable messenger cable, or by burying or by installation in metal conduit. When suspended, distance between supports shall not exceed twenty feet and they shall be so placed that they do not damage the cable jacket. When hung in a haulage entry containing a trolley wire, the cable shall be installed at least twelve inches from the trolley wire or feeder wires and away from the track.

(f) Any excess cable which is connected and supplying a load shall be coiled in a figure eight fashion, using long loops stored on a reel, or otherwise stored, at a place near the load where it can be protected by dangering off the place. Such cable shall not exceed one thousand feet in length.

(g) Frames and enclosures of high voltage switch units, transformers, metallic cable couplers, and splice boxes shall be grounded to the common or primary ground for the system in the high voltage cable.

(h) Taps or branch circuits from the high voltage feeder shall be made through circuit breakers adequate to interrupt any fault current which might occur. Relaying protection on such breakers shall include instantaneous and inverse time limit phase overcurrent, undervoltage, ground-fault and ground-continuity check-functions. A separate ground-continuity check-circuit originating at the branch circuit breaker shall be extended into each branch and shall be connected to ground at the frame of the load served. The ground-continuity check-circuit shall be so wired that the ground-wire or ground-continuity conductor or any connection on either wire cannot be broken without interrupting the check-circuit unless such break occurs on a branch which has been disconnected. A suitable load break switch may be used in lieu of a circuit breaker provided that the ground-continuity check-circuit shall be wired as provided in subsection (h) of this section.

(i) When nonload breaking disconnect switches are used for sectionalizing high voltage circuits, they shall be fully metal-clad, equipped with a door interlock to break the ground-continuity check-circuit, thus tripping the feeding breaker when the door is open, and a voltmeter or indicating light¹ to verify that the circuit is de-energized before the disconnect switches are opened.