30 CFR § 75.507-1
Electric equipment other than power-connection points; outby the last open crosscut; return air; permissibility requirements.
(a) All electric equipment, other than power-connection points, used
in return air outby the last open crosscut in any coal mine shall be
permissible except as provided in paragraphs (b) and (c) of this section.
(b) Notwithstanding the provisions of paragraph (a) of this section,
in any coal mine where nonpermissible electric face equipment may be taken
into or used inby the last open crosscut until March 30, 1974, such
nonpermissible electric face equipment may be used in return air outby the
last open crosscut.
(c) Notwithstanding the provisions of paragraph (a) of this section,
in any coal mine where a permit for noncompliance is in effect,
nonpermissible electric face equipment specified in such permit for
noncompliance may be used in return air outby the last open crosscut for the
duration of such permit.
[38 FR 4975, Feb. 23, 1973]