MSHA - Code of Federal Regulations - 30 CFR 75.800-2
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MSHA - Title 30 CFR
30 CFR § 75.800-2
Approved circuit schemes.
The following circuit schemes will be regarded as providing the necessary protection to the circuits required by §75.800:
(a) Ground check relays may be used for undervoltage protection if the relay coils are designed to trip the circuit breaker when line voltage decreases to 40 percent to 60 percent of the nominal line voltage;
(b) Ground trip relays on resistance grounded systems will be acceptable as grounded phase protection;
(c) One circuit breaker may be used to protect two or more branch circuits, if the circuit breaker is adjusted to afford overcurrent protection for the smallest conductor.