---
kind: "section"
citation: "46 C.F.R. § 111.50-3"
title: "46"
number: "111.50-3"
heading: "Protection of conductors."
url: "https://uscodex.org/cfr/46/111.50-3"
---

# §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:
  - (1) Propulsion circuits, [subpart 111.35](/cfr/46/subpart111.35.md).
  - (2) Steering circuits, [subpart 58.25](/cfr/46/subpart58.25.md) of this chapter.
  - (3) Motor circuits, [subpart 111.70](/cfr/46/subpart111.70.md).
  - (4) Flexible cord and fixture wire for lighting circuits, [subpart 111.75](/cfr/46/subpart111.75.md).
  - (5) Switchboard circuits, [subpart 111.30](/cfr/46/subpart111.30.md).
- (c) **Fuses and circuit breakers.** If the allowable current-carrying capacity of the conductor does not correspond to a standard rating for fuses or circuit breakers that meets [Section 240.6](/cfr/46/240.6.md) of NFPA 70 (incorporated by reference; see [46 CFR 110.10-1](/cfr/46/110.10-1.md)), then the next larger such rating is acceptable, except that:
  - (1) This rating must not be larger than 150 percent of the current-carrying capacity of the conductor; and
  - (2) 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.** No thermal cutout, thermal relay, or other device not designed to open a short circuit may 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 NFPA 70 or in IEC 60092-202:2016 (both incorporated by reference; see [§ 110.10-1](/cfr/46/110.10-1.md) of this subchapter).
- (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 [§ 111.05-17](/cfr/46/111.05-17.md) for the bus-tie feeder connecting the emergency and main switchboards; and
  - (2) **For motor-running protection described in Article 430 of NFPA 70 or in IEC 60092-202—** 2016 (both incorporated by reference; see [§ 110.10-1](/cfr/46/110.10-1.md) of this subchapter).

## Notes

### Amendments

[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; USCG-2003-16630, 73 FR 65197, Oct. 31, 2008; USCG-2013-0671, 78 FR 60153, Sept. 30, 2013; USCG-2020-0075, 88 FR 16362, Mar. 16, 2023]

### Authority

Authority: 46 U.S.C. 3306, 3703; DHS Delegation No. 00170.1, Revision No. 01.2. Section 111.05-20 and Subpart 111.106 also issued under sec. 617, Pub. L. 111-281, 124 Stat. 2905.

### Source

Source: CGD 74-125A, 47 FR 15236, Apr. 8, 1982, unless otherwise noted.

### Amendments

[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; USCG-2003-16630, 73 FR 65197, Oct. 31, 2008; USCG-2013-0671, 78 FR 60153, Sept. 30, 2013; USCG-2020-0075, 88 FR 16362, Mar. 16, 2023]