30 CFR § 56.12013
Splices and repairs of power cables.
Permanent splices and repairs made in power cables, including the ground
conductor where provided, shall be:
(a) Mechanically strong with electrical conductivity as near as
possible to that of the original;
(b) Insulated to a degree at least equal to that of the original, and
sealed to exclude moisture; and
(c) Provided with damage protection as near as possible to that of
the original, including good bonding to the outer jacket.