30 CFR § 77.800
High-voltage circuits; circuit breakers.
High-voltage circuits supplying power to portable or mobile equipment shall
be protected by suitable circuit breakers of adequate interrupting capacity
which are properly tested and maintained and equipped with devices to
provide protection against under voltage, grounded phase, short circuit and
overcurrent. High-voltage circuits supplying power to stationary equipment
shall be protected against overloads by either a circuit breaker or fuses of
the correct type and capacity.