Program Policy Manual - VOLUME V - Mine Safety and Health ...
Program Policy Manual - VOLUME V - Mine Safety and Health ...
Program Policy Manual - VOLUME V - Mine Safety and Health ...
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MSHA PROGRAM POLICY MANUAL <strong>VOLUME</strong> V<br />
A high-voltage cable coupler, switch, or other device not<br />
designed for load-breaking duty that is located at the bottom of<br />
a shaft or borehole may be used in conjunction with a highvoltage<br />
circuit breaker located on the surface provided:<br />
1. A remote control switch that, when activated, will open<br />
the circuit breaker is provided at the bottom of the<br />
shaft or borehole; <strong>and</strong><br />
2. A visual or audible means to indicate that the circuit<br />
breaker has opened when the remote control switch is<br />
activated is provided at the bottom of the shaft or<br />
borehole. Signal lights will be acceptable if the lights<br />
receive power through the auxiliary contacts on the<br />
circuit breaker.<br />
Unless fuse-type <strong>and</strong> knife-blade cutout switches are designed for<br />
load-breaking duty on high-voltage circuits, such switches shall<br />
be used for a disconnecting means only when some other means is<br />
first used to deenergize the circuit.<br />
75.520 Electric Equipment; Switches<br />
All control devices shall be fully enclosed to prevent exposure<br />
of bare wires <strong>and</strong> energized parts. The use of plugs <strong>and</strong><br />
receptacles (e.g., Miller plugs), trolley taps, <strong>and</strong> trolley wire<br />
"stingers" to start <strong>and</strong> stop electric motors are examples of<br />
noncompliance with this Section.<br />
75.521 Lightning Arrester; Ungrounded <strong>and</strong> Exposed Power<br />
Conductors <strong>and</strong> Telephone Wires<br />
Conductors that are: (1) provided with metallic shields; (2)<br />
jacketed by a ground metal covering or enclosure; (3) installed<br />
under grounded metal framework; (4) buried in the earth; or (5)<br />
made of triplex or quadraplex that is supported by a grounded<br />
messenger wire, are not considered exposed for the length so<br />
protected. If the trolley wire of a d.c. system is paralleled by<br />
an exposed feeder cable, one lightning arrester would provide<br />
protection for both if they are connected together near the<br />
lightning arrester.<br />
Lightning arrester ground fields shall be maintained with as low<br />
a resistance to earth as possible, preferably less than 5 ohms<br />
<strong>and</strong> no more than 25 ohms. Lightning arrester ground fields shall<br />
be separated from neutral ground fields by at least 25 feet.<br />
This distance prevents lightning surges from being transmitted to<br />
the neutral ground field where they could momentarily energize<br />
the frames of equipment grounded to the neutral ground field.<br />
February 2003 (Release V-33) 67
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