(a) General rule.--Distribution centers may be used to distribute utilization power to portable equipment. The distribution center may be connected to the load center through one or more cables or conductors protected by flame-resistant jackets with combined capacity sufficient to carry the maximum loads that may be encountered. The distribution center shall contain breakers adequate to interrupt any fault current that might occur, which shall feed each unit of equipment that is connected to the distribution center. Each breaker shall be equipped with tripping devices that will function on overload, phase fault and ground fault. Distribution centers shall be located on intake air only and shall not be located beyond the last open crosscut or closer than 150 feet from pillar workings unless the distribution center shall have an approved explosion-proof enclosure.

(b) Cables.--Utilization voltage cables shall be fitted with plug couplers and provisions made so that cables cannot be uncoupled under load. All plugs and sockets shall be substantially constructed, and any exposed metal portions shall be grounded. Couplers shall be constructed so that the ground conductor connection is broken last during uncoupling.

(c) Ground conductors.--Utilization voltage conductors, cables or conductor groups shall contain one or more ground conductors which when combined shall be able to carry safely and continuously at least twice the maximum ground fault current.

(d) Option.--A combined alternating and direct-current distribution or load center complete within a substantially fireproof metal enclosure, with a dry-type transformer and solid state rectifier and adequate automatic electrical protection, may be used to distribute alternating and direct current utilization power. The power supply to this unit may be low, medium or high voltage. When high voltage is utilized, the requirements of section 332¹ shall apply. When medium or low voltage is utilized, this section shall apply. However, when an external DC distribution device is employed, the rectifier output may be taken through a main DC circuit breaker to that device without the use of a plug and receptacle system.