Pennsylvania Statutes Title 52 P.S. Mines and Mining § 690-332. Load center

(1) Connection of the high-voltage cable to the load center shall be made through a cable coupler of the type described in section 331(c). 1

(2) The load center shall be equipped with a positive disconnect means on the incoming or high-voltage circuit. This may consist of a circuit breaker, load-break switch, disconnect switch or other device. The following apply:

(3) The restriction of section 330(4)  2 pertaining to transformer connections and use of zig-zag grounding transformers also apply to the load center.

(4) The transformer secondary neutral, direct or derived, shall be connected to machine trailing cable safety ground conductors through a ground current limiting resistor capable of limiting ground fault current to 25 amperes or less. The inby side of the resistor shall be grounded to the load center frame if no DC equipment powered from a common mine DC system can contact the frames of AC equipment powered by this load center. In the event there is a possibility of frame contact between AC equipment and DC equipment supplied from a common DC mine system, the inby side of the resistor may be insulated from the load center frame and shall be solidly connected to the DC ground system.

(5) The load center shall be equipped with a main secondary breaker of adequate interrupting capacity with tripping devices which shall feed individual machine breakers located either in the load center or external to it in a separate distribution center. External utilization voltage connections shall be made through receptacles arranged so that they cannot be uncoupled under load.

(6) Load centers shall be located on intake air only. Load centers shall not be located beyond the last open crosscut or located closer than 250 feet along the air route to pillar workings.