[Code of Federal Regulations] [Title 46, Volume 4] [Revised as of October 1, 2002] From the U.S. Government Printing Office via GPO Access [CITE: 46CFR111.50-3] [Page 230] TITLE 46--SHIPPING CHAPTER I--COAST GUARD, DEPARTMENT OF TRANSPORTATION (CONTINUED) PART 111--ELECTRIC SYSTEMS--GENERAL REQUIREMENTS--Table of Contents Subpart 111.50--Overcurrent Protection Sec. 111.50-3 Protection of conductors. (a) Purpose. The purpose of overcurrent protection for conductors is to open the electric circuit if the current reaches a value that will cause an excessive or dangerous temperature in the conductor or conductor insulation. A grounded conductor is protected from overcurrent if a protective device of a suitable rating or setting is in each ungrounded conductor of the same circuit. (b) Overcurrent protection of conductors. Each conductor must be protected in accordance with its current carrying capacity, except a conductor for the following circuits which must meet the following listed subparts of this chapter: (1) Propulsion circuits, Subpart 111.35. (2) Steering circuits, subchapter F of this chapter. (3) Motor circuits, Subpart 111.70. (4) Flexible cord and fixture wire for lighting circuits, Subpart 111.75. (5) Switchboard circuits, Subpart 111.30. (c) Fuses and circuit breakers. If the allowable current carrying capacity of the conductor does not correspond to a standard fuse or circuit breaker rating which meets article 240-6 of the NEC or IEC 92- 202 and the next larger standard fuse or circuit breaker rating is used, it must not be larger than 150 percent of the current carrying capacity of the conductor. The effect of temperature on the operation of fuses and thermally controlled circuit breakers must be taken into consideration. (d) Parallel overcurrent protective devices. An overcurrent protective device must not be connected in parallel with another overcurrent protective device. (e) Thermal devices. A thermal cutout, thermal relay, or other device not designed to open a short circuit, must not be used for protection of a conductor against overcurrent due to a short circuit or ground, except in a motor circuit as described in Article 430 of the National Electrical Code or in IEC 92-202. (f) Ungrounded conductors. A fuse or overcurrent trip unit of a circuit breaker must be in each ungrounded conductor. A branch switch or circuit breaker must open all conductors of the circuit, except grounded conductors. (g) Grounded conductor. An overcurrent device must not be in a permanently grounded conductor, except: (1) An overcurrent device that simultaneously opens all conductors of the circuit, unless prohibited by Sec. 111.05-17 for the bus-tie feeder connecting the emergency and main switchboards; and (2) For motor-running protection described in Article 430 of the National Electrical Code or in IEC 92-202. [CGD 74-125A, 47 FR 15236, Apr. 8, 1982, as amended by CGD 94-108, 61 FR 28279, June 4, 1996; CGD 97-057, 62 FR 51047, Sept. 30, 1997]