30 CFR § 75.603
Temporary splice of trailing cable.
One temporary splice may be made in any trailing cable. Such trailing cable
may only be used for the next 24-hour period. No temporary splice shall be
made in a trailing cable within 25 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
section, the term "splice" means the mechanical joining of one or more
conductors that have been severed.