[Code of Federal Regulations]

[Title 30, Volume 1]

[Revised as of July 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 30CFR18.50]



[Page 110]

 

                       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.