(a) 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 which may be encountered. The distribution center shall contain breakers adequate to interrupt any fault current which might occur, which shall feed each unit of equipment which is connected to the distribution center. Each breaker shall be equipped with tripping devices which will function on overload, phase fault and ground fault. Distribution centers shall be located on intake air only, and shall not be located beyond one hundred fifty feet outside the last open crosscut unless the distribution center shall have an approved explosion-proof enclosure.

(b) Utilization voltage cables shall be fitted with plug couplers and provision made so that cables cannot be uncoupled under load. All plugs and length of cable 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) Utilization voltage conductors, cables, or conductor groups shall contain one or more ground conductors which combined equal one-half size of power conductor or shall be able to carry safely and continuously at least twice the maximum ground fault current.