30 CFR § 57.12088
Splicing trailing cables.
No splice, except a vulcanized splice or its equivalent, shall be made in a
trailing cable within 25 feet of the machine unless the machine is equipped
with a cable reel or other power feed cable payout-retrieval system. However,
a temporary splice may be made to move the equipment for repair.
Subpart L--Compressed Air and Boilers