[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: 46CFR111.12-11]

[Page 221]
 
                           TITLE 46--SHIPPING
 
    CHAPTER I--COAST GUARD, DEPARTMENT OF TRANSPORTATION (CONTINUED)
 
PART 111--ELECTRIC SYSTEMS--GENERAL REQUIREMENTS--Table of Contents
 
           Subpart 111.12--Generator Construction and Circuits
 
Sec. 111.12-11  Generator protection.

    (a) Applicability. This section applies to each generator except a 
propulsion generator.
    (b) General. Each ship's service generator and emergency generator 
must be protected by an individual, tripfree, air circuit breaker whose 
tripping characteristics can be set or adjusted to closely match the 
generator capabilities and meet the coordination requirements of Subpart 
111.51. Each circuit breaker must contain the trips required by this 
section.
    (c) Type of trips. A circuit breaker for a generator must:
    (1) Open upon the shutting down of the prime mover;
    (2) Have longtime overcurrent trips or relays set as necessary to 
coordinate with the trip settings of the feeder circuit breakers; and
    (3) Not have an instantaneous trip with the exception that an 
instantaneous trip is required if:
    (i) Three or more alternating-current generators can be paralleled; 
or
    (ii) The circuit breaker is for a direct current generator.
    (d) Setting of longtime overcurrent trips. The pickup setting of the 
longtime overcurrent trip of a generator circuit breaker must not be 
larger than:
    (1) 115 percent of the generator rating for a continuous rated 
machine; or
    (2) 115 percent of the overload rating for a machine with a 2-hour 
or greater overload rating.
    (e) Setting of instantaneous trips. The instantaneous trip of a 
generator circuit breaker must be set above, but as close as practicable 
to, the maximum asymmetrical short circuit available from any one of the 
generators that can be paralleled.
    (f) Reverse-power and reverse-current trips. Each generator arranged 
for parallel operation must have reverse-power or reverse-current trips.
    (g) Location. A ship's service generator overcurrent protective 
device must be on the ship's service generator switchboard. The 
generator and its switchboard must be in the same space. (For the 
purposes of this section, the following are not considered separate from 
the machinery space: (1) A control room that is inside of the machinery 
casing and (2) a dedicated switch-gear and semiconductor rectifier (SCR) 
compartment on a mobile offshore drilling unit that is separate from but 
directly adjacent to and on the same level as the generator room).
    (h) Three-wire, single-phase and four-wire, three-phase generators. 
There must be circuit breaker poles for each generator lead, except in 
the neutral lead.
    (i) Three-wire, direct-current generators. Each three-wire, direct 
current generator must meet the following requirements:
    (1) Circuit breaker poles. There must be separate circuit breaker 
poles for the positive and negative leads, and, unless the main poles 
provide protection, for each equalizer lead. If there are equalizer 
poles for a three-wire generator, each overload trip must be of the 
``Algebraic'' type. If there is a neutral pole in the generator circuit 
breaker, there must not be an overload trip element for the neutral 
pole. In this case, there must be a neutral overcurrent relay and alarm 
system that is set to function at a current value not more than the 
neutral rating.
    (2) Equalizer buses. For each three-wire generator, the circuit 
breaker must protect against a short circuit on the equalizer bus.
    (j) Circuit breaker reclosing. Generator circuit breakers must not 
automatically close after tripping.

[CGD 74-125A, 47 FR 15236, Apr. 8, 1982, as amended by CGD 81-030, 53 FR 
17847, May 18, 1988; CGD 94-108, 61 FR 28277, June 4, 1996; 62 FR 23908, 
May 1, 1997]