Section 70-1135 - 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 subsection (c) of section 1134. (2) The load center shall be equipped with 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.(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 subsection (5) of section 1132 of article XI pertaining to transformer connections and use of "zig-zag" grounding transformers also apply to the load center.(4) The transformer secondary neutral of load center transformers, 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 twenty-five amperes or less. The inby side of this resistor shall be grounded to the load center frame.(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 so arranged that they cannot be uncoupled under load.(6) Load centers shall be located on intake air only. Load centers shall not be located beyond one hundred fifty feet outside the last open crosscut.1965, Nov. 10, P.L. 721, No. 346, art. XI, § 1135.