30 CFR § 18.42 Explosion-proof distribution boxes.
(a) A cable passing through an outside wall(s) of a distribution box
shall be conducted either through a packing gland or an interlocked plug and
receptacle.
(b) Short-circuit protection shall be provided for each branch
circuit connected to a distribution box. The current-carrying capacity of the
specified connector shall be compatible with the automatic
circuit-interrupting device.
(c) Each branch receptacle shall be plainly and permanently marked to
indicate its current-carrying capacity and each receptacle shall be such that
it will accommodate only an appropriate plug.
(d) Provision shall be made to relieve mechanical strain on all
connectors to distribution boxes.
