Wyoming Administrative Code › Agency 053 - Workforce Services, Department of › Sub-Agency 0004 - Mining Inspector › Chapter 4 - UNDERGROUND COAL MINES › Subpart H - Grounding › Section 75.703-3 - Approved methods of grounding offtrack mobile, portable and stationary direct-current machines

Current through July 13, 2024
In grounding off track direct-current machines and the
					 enclosures of their component parts, the following methods of grounding will
					 meet the requirements of S 75.703:
(a)
				  The use of a separate grounding conductor located within the trailing cable of
				  mobile and portable equipment and connected between such equipment and the
				  direct-current grounding medium;
(b) The use of a separate ground conductor
				  located within the direct-current power cable feeding stationary equipment and
				  connected between such stationary equipment and the direct-current grounding
				  medium;
(c) The use of a separate
				  external ground conductor connected between stationary equipment and the
				  direct-current grounding medium; or,
(d) The use of silicon diodes; however, the
				  installation of such devices shall meet the following minimum requirements:
(1) Installation of silicon diodes shall be
				  restricted to electric equipment receiving power from a direct-current system
				  with one polarity grounded;
(2)
				  Where such diodes are used on circuits having a nominal voltage rating of 250,
				  they must have a forward current rating of 400 amperes or more, and have a peak
				  inverse voltage rating of 400 or more;
(3) Where such diodes are used on circuits
				  having a nominal voltage rating of 550, they must have a forward current rating
				  of 250 amperes or more, and have a peak inverse voltage rating of 800 or
				  more;
(4) Where fuses approved by
				  the Secretary are used at the outby end of a trailing cable connected to
				  electrical equipment employing silicon diodes, the rating of such fuses must
				  not exceed 150 percent of the nominal current rating of the grounding
				  diodes;
(5) Where circuit breakers
				  are used at the outby end of a trailing cable connected to electrical equipment
				  employing silicon diodes, the instantaneous trip setting shall not exceed 300
				  percent of the nominal current rating of the grounding diode;
(6) Overcurrent devices must be used and
				  installed in such a manner that the operating coil circuit of the main
				  contactor will open when a fault current with a value of 25 percent or less of
				  the diode rating flows through the diode;
(7) The silicon diode installed must be
				  suitable to the grounded polarity of the power system in which it is used and
				  its threaded base must be solidly connected to the machine frame on which it is
				  installed;
(8) In addition to the
				  grounding diode, a polarizing diode must be installed in the machine control
				  circuit to prevent operation of the machine when the polarity of a trailing
				  cable is reversed;
(9) When
				  installed on permissible equipment, all grounding diodes, over current devices,
				  and polarizing diodes must be placed in explosion proof compartments;
(10) When grounding diodes are installed on a
				  continuous miner, their nominal diode current rating must be at least 750
				  amperes or more; and,
(11) All
				  grounding diodes shall be tested, examined and maintained as electrical
				  equipment in accordance with the provisions of S 75.512.