Pennsylvania Statutes Title 52 P.S. Mines and Mining § 70-1113. Switches, fuses and circuit breakers

(a) Fuses and automatic circuit breakers shall be so 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, adjustable to trip at from fifty percent to one hundred fifty percent of their normal rated capacity.

(b) Circuit breakers used to protect feeder circuits shall be set to trip when the current exceeds by more than fifty percent the current carrying 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 longer period than ten seconds. Trip current shall be indicated at the circuit breaker.

(c) 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 person authorized by the mine foreman. Wire or other conducting materials shall not be used as a substitute for properly designed fuses.

(d) Fuses used to protect feeders shall not be greater than the current rating of the feeder.

(e) All switches, circuit breakers and fuses shall have incombustible bases.

(f) Operating controls, such as starters, switches and switch buttons, shall be so installed that they are readily accessible and can be operated without danger of contact with moving or live parts. On stationary equipment provision shall be made for locking starting equipment in “off” position to prevent accidental application of power.

(g) Circuit breakers and disconnect switches shall be installed underground in all main power circuits within five hundred feet of the bottom of shafts, boreholes and inclines, where main power circuits enter the mine.