(a) Construction.--Fuses and automatic circuit breakers shall be constructed as to effectively interrupt the current on short circuit or when the current through them exceeds a predetermined value. Open type fuses shall be provided with terminals. Circuit breakers shall be of adequate interrupting capacity.

(b) Trip setting.--Circuit breakers used to protect feeder circuits shall be set to trip when the current exceeds more than 50% of the rated capacity of the feeder. In case the feeder is subjected to overloads sufficient to trip the circuit breaker but of short duration, the circuit breaker may be equipped with a device which will prevent its acting unless the overload persists for a period longer than ten seconds. Trip current shall be indicated at the circuit breaker.

(c) Fuses.--Fuses shall be stamped or marked or shall have a label attached indicating the maximum current which they are intended to carry. Fuses shall only be adjusted or replaced by a competent individual authorized by the mine foreman.

(d) Protective fuses.--Fuses used to protect feeders shall be a less current rating than the feeder.

(e) Incombustible base requirement.--All switches, circuit breakers and fuses shall have incombustible bases.