83 STAT. ]
PUBLIC LAW 91-173-DEC. 30, 1969
779
(o) All electric equipment shall be provided with switches or other controls that are safely designed, constructed, and installed. (p) Each ungrounded, exposed power conductor that leads underground shall be equipped with suitable lightning arresters of approved type within one hundred feet of the point where the circuit enters the mine. Lightning arresters shall be connected to a low resistance grounding medium on the surface which shall be separated from neutral grounds by a distance of not less than twenty-five feet. (q) Xo device for the purpose of lighting any coal mine which has not been approved by the Secretary or his authorized representative shall be permitted in such mine. (r) An authorized representative of the Secretary may require in any mine that electric face equipment be provided with devices that will permit the equipment to be deenergized quickly in the event of an emergency. TRAILING
CABLES
SEC. 306. (a) Trailing cables used in coal mines shall meet the requirements established by the Secretary for flame-resistant cables. (b) 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. (c) When two or more trailing cables junction to the same distribution center, means shall be provided to assure against connecting a trailing cable to the wrong size circuit breaker. (d) One temporary splice may be made in any trailing cable. Such trailing cable may only be used tor the next twenty-four hour period. No temporary splice shall be made in a trailing cable within twentyfive feet of the machine, except cable reel equipment. Temporary splices in trailing cables shall be made in a workmanlike manner and shall be mechanically strong and well insulated. Trailing cables or hand cables which have exposed wires or which have splices that heat or spark under load shall not be used. As used in this subsection, the term "splice" means the mechanical joining of one or more conductors that have been severed. (e) When permanent splices in trailing cables are made, they shall be— (1) mechanically strong with adequate electrical conductivity and flexibility; (2) effectively insulated and sealed so as to exclude moisture; and (3) vulcanized or otherwise treated with suitable materials to provide flame-resistant qualities and good bonding to the outer jacket. (f) Trailing cables shall be clamped to machines in a manner to protect the cables from damage and to prevent strain on the electrical connections. Trailing cables shall be adequately protected to prevent damage by mobile equipment. (g) Trailing cable and power cable connections to junction boxes shall not be made or broken under load.
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