Program Policy Manual - VOLUME V - Mine Safety and Health ...

MSHA PROGRAM POLICY MANUAL VOLUME V
2. Either the ground wire is broken at any point, or the
impedance of the grounding circuit increases beyond
the amount necessary to cause a 100-volt drop in the
grounding circuit external to the grounding resistor
under ground fault conditions.
It shall not be possible to reclose the circuit breaker while
either of the above faults exist.
This Section permits the approval of a no less effective device in
lieu of a fail safe ground check circuit. The following alternate
method shall be considered no less effective than a fail safe
ground check circuit for assuring the continuity of the grounding
circuit extending to permanently installed stationary equipment
which is supplied power from a high-voltage resistance-grounded
system:
1. An equipment grounding conductor, sized in accordance with
Section 77.701-3, shall originate at the grounded side of
the grounding resistor and shall extend along with the
power conductors and shall serve as a grounding conductor
for the frames of all equipment receiving power from the
resistance-grounded system.
2. A grounding electrode conductor shall connect the frames
of the stationary equipment to a low resistance ground
field located near the utilization location.
3. The ohmic value of the grounding resistor and the
impedance of the low resistance ground field shall be
maintained in such a manner that not more than 100 volts
will appear between the equipment frame and earth under
fault conditions in the event that the equipment grounding
conductor should be severed.
4. The ohmic value of the grounding resistor and the
impedance of the ground field to which the grounding
resistor is grounded shall be maintained in such manner
that not more than 100 volts will appear between the
grounded side of the grounding resistor and earth under
fault conditions in the event that the equipment grounding
conductor should be severed.
5. This method for assuring the continuity of grounding
circuits shall not be approved for high-voltage circuits
which supply power to high-voltage equipment underground
in a mine or to portable or mobile high-voltage equipment
on the surface. The continuity of such grounding circuits
shall be continuously monitored by fail safe ground check
February 2003 (Release V-33) 190