(a) General requirement. Power and lighting circuits on towing vessels must be protected by suitable overcurrent protection.

(b) Specific requirements.

(1) Cable and wiring used in power and lighting circuits must have overcurrent protection that opens the circuit at the standard setting closest to 80 percent of the manufacturer's listed ampacity. Overcurrent protection setting exceptions allowed by NFPA's National Electrical Code (NEC), Article 240 (incorporated by reference, see §136.112 of this subchapter) may be employed.

(2) If the manufacturer's listed ampacity is not known, tables referenced in Article 310.15(B) of the NEC (incorporated by reference, see §136.112 of this subchapter) must be used, assuming a temperature rating of 75 °C and an assumed temperature of 50 °C for machinery spaces and 40 °C for other spaces.

(3) Overcurrent protection devices must be installed in a manner that will not open the path to ground in a circuit; only ungrounded conductors must be protected. Overcurrent protection must be coordinated such that an overcurrent situation is cleared by the circuit breaker or fuse nearest to the fault.

(4) Each transformer must have protection against overcurrent that meets Article 450 of the NEC (incorporated by reference, see §136.112 of this subchapter).

(5) On a towing vessel, other than an excepted vessel as defined in §136.110 of this subchapter, essential systems and non-essential systems must not be on the same circuit or share the same overcurrent protective device.