46 CFR § 120.380 - Overcurrent protection.
(a) Overcurrent protection must be provided for each ungrounded conductor for the purpose of opening the electric circuit if the current reaches a value that causes an excessive or dangerous temperature in the conductor or conductor insulation.
(b) The grounded conductor of a circuit must not be disconnected by a switch or circuit breaker, unless the ungrounded conductors are simultaneously disconnected.
(c) A conductor of a control, interlock, or indicator circuit, such as a conductor for an instrument, pilot light, ground detector light, or potential transformer, must be protected by an overcurrent device.
(d) Conductors must be protected in accordance with their current carrying capacities. If the allowable current carrying capacity does not correspond to a standard device size, the next larger overcurrent device may be used provided it does not exceed 150 per cent of the conductor current carrying capacity.
(e) Steering gear control system circuits must be protected against short circuit.
(g) Each lighting branch circuit must be protected against overcurrent either by fuses or circuit breakers rated at not more than 30 amperes.
(h) Overcurrent devices capable of carrying the starting current of the motor must be installed to protect motors, motor conductors, and control apparatus against:
(1) Overcurrent due to short circuits or ground faults; and
(2) Overload due to motor running overcurrent, in accordance with § 111.70–1 in subchapter J of this chapter. A protective device integral with the motor, which is responsive to both motor current and temperature, may be used.
(i) An emergency switch must be provided in the normally ungrounded main supply conductor from a battery. The switch must be accessible and located as close to the battery as practicable.
(j) Disconnect means must be provided on the supply side of and adjacent to all fuses for the purpose of de-energizing the fuses for inspection and maintenance purposes.
(k) If the disconnect means is not within sight of the equipment that the circuit supplies, means must be provided for locking the disconnect device in the open position.
(m) Each circuit breaker must meet UL 489, “Molded-Case Circuit Breakers and Circuit Breaker Enclosures,” or other standard specified by the Commandant, and be of the manually reset type designed for:
(1) Inverse time delay;
(2) Instantaneous short circuit protection; and
(3) Switching duty if the breaker is used as a switch.
(n) Each circuit breaker must indicate whether it is in the open or closed position.