30 CFR § 75.822
Underground high-voltage longwall cables.
In addition to the high-voltage cable design specifications in
of this part, high-voltage cables for use on longwalls may
be a type SHD cable with a center ground-check conductor no smaller
than a No. 16 AWG stranded conductor. The cables must be MSHA accepted
as flame-resistant under part 18 or approved under subpart K of part 7.