30 CFR § 57.12013
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.