Section 690-332 - Load centerTransmission voltage shall be reduced to machine utilization voltage by a portable transformer or load center of adequate capacity for the equipment powered by it. The transformer shall be of the dry type, ventilated, nonventilated or sealed, substantially constructed and completely enclosed in a metal case. The metal enclosure shall be connected to the high-voltage system ground conductor in the high-voltage cable. Complete load center construction shall render it essentially fireproof. In addition to these requirements, the following shall be observed:
(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) . (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:(i) If a circuit breaker is used for this purpose, it shall be equipped with instantaneous and inverse time limit phase overcurrent and undervoltage relaying protection.(ii) If a device other than a circuit breaker is used, it shall be so arranged that it cannot be operated until the ground-continuity check circuit in the high-voltage cable has opened causing the nearest feeding circuit breaker to trip.(3) The restriction of section 330(4) 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.2008, July 7, P.L. 654, No. 55, §332, effective in 180 days [ 1/5/2009].