30 CFR § 77.600
Trailing cables; short-circuit protection; disconnecting devices.
Short-circuit protection for trailing cables shall be provided by an
automatic circuit breaker or other no less effective device, approved by the
Secretary, of adequate current-interrupting capacity in each ungrounded
conductor. Disconnecting devices used to disconnect power from trailing
cables shall be plainly marked and identified and such devices shall be
equipped or designed in such a manner that it can be determined by visual
observation that the power is disconnected.