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

MSHA PROGRAM POLICY MANUAL VOLUME V
2. Second grounding circuit shall connect the frames of the
stationary equipment to a low resistance ground field
located near the utilization location.
3. The resistance of the grounding resistor and the resistance
of the 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 grounding conductor should be severed.
75.803-2 Ground Check Systems not Employing Pilot Check Wires;
Approval by the Secretary
Wireless ground check circuits shall not be approved unless such
circuits are tested and evaluated by Technical Support.
75.804 Underground High-Voltage Cables
This Section does not apply to cables of ungrounded high-voltage
circuits that are enclosed in steel armor or rigid steel conduit.
All high-voltage cables, whether single or multiple conductor,
shall conform to this Section.
If single-conductor high-voltage cables are used, the cables
should be installed on a well-supported messenger wire or on cable
hangers, and a power grounding conductor and ground check
conductor shall extend along with the power conductors. The
messenger wire, when paralleled with the cable shielding, can
serve as the grounding conductor for the circuit if the impedance
of the grounding circuit is low enough to limit the voltage drop
to 100 volts or less. Normally, the high resistance of steel
messenger wire will limit the distance the circuit can be
extended. The shielding shall be connected to the messenger wire
at each splice (single-conductor cables) and, at each termination.
Inspectors must calculate the parallel resistance of the messenger
wire and the three shields when determining compliance with the
requirement for a maximum voltage drop of 100 volts.
Cables in systems using "other no less effective device approved
by the Secretary or his authorized representative" as provided for
in Section 75.803 for assuring grounding circuit continuity are
exempted from the requirement to have an insulated ground check
conductor.
75.805 Couplers
An existing high-voltage coupler that is not equipped with a pin
for the ground check circuit may be used if a locking switch is
mounted on the coupler so that it cannot be uncoupled until the
key is inserted in the lock and the switch is opened. This
operation breaks the ground check conductor first. Several
February 2003 (Release V-33) 79