Section 43.31. Underground stations and transformer rooms

(a) Mounting. All switches, circuit breakers, rheostats, fuses and measuring instruments used in connection with underground motor generators, rotary converters, transformers, and motors shall be mounted on standard bases of noncombustible and insulating material, but in no case shall primary instruments be used in circuits of more than 300 volts. This requirement shall not apply to compensators for induction motors. The switches, circuit breakers, rheostats, fuses and instruments may be mounted on a common base, if the base is of noncombustible, insulating material.

(b) Passageways. A passageway at least 3 feet in width shall be maintained in front of all switchboards. No one shall be permitted in back of the switchboards while the current is on.

(c) Switchboards. Any space over 30 inches wide at the back of switchboards shall be accessible from each end and shall be kept locked up in case of medium and high voltage boards, but no lock shall be used that will not permit the door to be opened from the inside without the use of a key. In no case shall this space be used as a change room, wardrobe, or for the storage of material. Only noncombustible flooring shall be used at the front and back of high voltage boards, and insulating mats or their equivalent shall be provided in front and back of all boards, whatever the voltage.

(d) Conductors. No electric conductor shall cross a passageway at the back of a switchboard except below the floor or at a height of not less than seven feet above the level of the floor, unless properly guarded.

(e) Live metal work. No live metal work shall be placed on the front of a high voltage switchboard within 7 feet of the floor, unless properly guarded.

(f) Terminals. All exposed terminals on underground machines shall be protected with properly designed insulating covers of suitable materials or with metal covers connected to ground.

(g) Transformer rooms. Transformer rooms shall be properly lighted and of fireproof construction, and, if of conductive material, shall be effectively grounded.

(h) Circuits. Circuits leaving the transformers shall be protected by a switch and an automatic circuit breaker to interrupt current, but fuses may be substituted for the circuit breakers. Primary fuses and disconnecting switches shall be placed in the primary circuit ahead of the transformers.