[Code of Federal Regulations]
[Title 30, Volume 1]
[Revised as of July 1, 2002]
From the U.S. Government Printing Office via GPO Access
[CITE: 30CFR18.50]

[Page 104]
 
                       TITLE 30--MINERAL RESOURCES
 
  CHAPTER I--MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR
 
PART 18--ELECTRIC MOTOR-DRIVEN MINE EQUIPMENT AND ACCESSORIES--Table of Contents
 
             Subpart B--Construction and Design Requirements
 
Sec. 18.50  Protection against external arcs and sparks.

    Provision shall be made for maintaining the frames of all off-track 
machines and the enclosures of related detached components at safe 
voltages by using one or a combination of the following:
    (a) A separate conductor(s) in the portable cable in addition to the 
power conductors by which the machine frame can be connected to an 
acceptable grounding medium, and a separate conductor in all cables 
connecting related components not on a common chassis. The cross-
sectional area of the additional conductor(s) shall not be less than 50 
percent of that of one power conductor unless a ground-fault tripping 
relay is used, in which case the minimum size may be No. 8 (AWG). Cables 
smaller than No. 6 (AWG) shall have an additional conductor(s) of the 
same size as one power conductor.
    (b) A means of actuating a circuit-interrupting device, preferably 
at the outby end of the portable cable.
    Note: The frame to ground potential shall not exceed 40 volts.
    (c) A device(s) such as a diode(s) of adequate peak inverse voltage 
rating and current-carrying capacity to conduct possible fault current 
through the grounded power conductor. Diode installations shall include: 
(1) An overcurrent device in series with the diode, the contacts of 
which are in the machine's control circuit; and (2) a blocking diode in 
the control circuit to prevent operation of the machine with the 
polarity reversed.