BOATBUILDER'S HANDBOOK

Electrical Systems - Manufacturer Requirements


FEDERAL LAW

183.460 - Overcurrent Protection: Special Applications

(a) Each ungrounded output conductor from a storage battery must have a manually reset, trip-free circuit breaker or fuse, unless the supply conductor is in the main power feed circuit from the battery to an engine cranking motor. The circuit breaker or fuse must be within 72 inches of the battery measured along the conductor, unless, for boats built prior to August 1, 1985, the circuit has a switch that disconnects the battery.

 

Ungrounded conductors connected to a storage battery, other than cranking motor conductors, must have overcurrent protection in accordance with 183.455(a). This section of the regulation provides an exception to 183.455(b) which allows the overcurrent protection location for the battery cable, as described, to be a distance from the connection at the battery (Section 182.455(b) requires the overcurrent protection to be at the power source). The distance from the battery connection depends on whether or not the overcurrent protection device is equipped with a switch.

  • Overcurrent protection without a switch must be located within 72 inches of the battery connection. See Figure 25.
  • Overcurrent protection with a switch may be located anywhere along the battery cable, if the boat was built before August 1, 1985. See Figure 25.

The only exception to the overcurrent protection requirement for conductors is for cranking motor power conductors, as excepted in 183.455(e). Schematics of typical main supply circuits are shown in Figure 25.
 

TO COMPLY WITH THE LAW

Except for the power supply conductors to the engine cranking motor:

  • Is there a manually reset, tripfree circuit breaker or fuse in each ungrounded output conductor from each storage battery?
  • Is the circuit breaker or fuse within 72 inches of the battery, measured along the conductor? or
  • If the boat was built prior to August 1, 1985, is there a switch in the circuit to disconnect the battery?



FEDERAL LAW

183.460 - Overcurrent Protection: Special Applications

(b) Each ungrounded output conductor from an alternator or generator, except for self-limiting alternators or generators, must have a circuit breaker or fuse that has a current rating that does not exceed 120 percent of the maximum rated current of the alternator or generator at 60° C.


The output of alternators or generators (AC or DC) must have overcurrent protection as described in 183.455. This must be by means of a circuit breaker or fuse rated at no more than 120% (1.2 times) of the maximum rated output current of the alternator or generator. As this output rating may be temperature sensitive, a 60° C (140° F) temperature is used as a standard (see Figure 27). The only exception to the breaker or fuse requirement is for "self limiting" alternators or generators. These are devices that are designed and manufactured to provide only a certain maximum output no matter how much load is applied (i.e. they cannot be overloaded). This information must be obtained from the alternator or generator manufacturer, or may be available on the nameplate.

NOTE:
Nameplates are good practice, but are not required by the regulation.

The "self limiting" concept can also be applied to certain battery chargers, magneto grounding circuits, and other similar components that provide electrical output for specific functions. This electrical output is limited by the construction of the electrical components no matter what the load, and when its output circuit is grounded, the voltage drops to zero.

The overcurrent protection requirements of section 183.455 apply to ungrounded conductors. For the purpose of these requirements, the conductors used with sender units such as fuel gauges, oil temperature switches, thermostats, etc., are considered to be grounded conductors and do not require overcurrent protection. The supply conductors to the gauge or other measuring systems are protected by overcurrent protection, and this indirectly protects the grounded conductors discussed above.

TO COMPLY WITH THE LAW

  • Is there a circuit breaker or fuse in each ungrounded output conductor from a non-self limiting alternator or generator?
  • Is the circuit breaker or fuse rated at no more than 120% of the maximum rated current of the alternator or generator at 60° C?


FIGURE 27 - Alternators and Generators

FIGURE 27 - Alternators and Generators (continued)


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