Answers to Some Common Questions
About Marine Circuit Protection
By Scott Renne


A boat owner should know some of the basics of electrical wiring and circuit protection before tackling any electrical projects aboard his craft.

Following are the answers to a few commonly asked questions about circuit protection that should help make these projects easier for the beginner.

What is circuit protection?

Circuit protection is the intentional installation of a "weak link", such as a fuse or circuit breaker, in an electrical circuit.

What do fuses and circuit breakers protect against?

They prevent excessive amperage from traveling through a wire, which can damage electrical and electronic equipment. Too much amperage can also cause a wire to overheat and melt or burn its insulation, causing a fire.

How much amperage can a wire safely carry?

The American Boat and Yacht Council (ABYC) publishes recommendations on how much amperage each size of wire should carry. For example, it says wire -- with 105'C insulation and conducting less than 50 volts in a non-engine space area -- can handle up to 20 amps if it is 18AWG gauge, 60 amps if 10AWG, 210 amps if 2AWG and 445 amps if 4/OAWG. For more details, contact the ABYC at 410-956-1050. If a wire is properly sized, why is a fuse or circuit breaker necessary? The circuit may become accidentally grounded, allowing a dangerous amount of amperage flow. Equipment failure, improper maintenance or an exposed wire contacting a grounded surface can cause this problem.

How does a fuse or circuit breaker stop the amperage flow?

They respond to the high heat or large magnetic field generated by excessive amperage. Fuses only respond to heat and have a special link that melts at high temperatures. Circuit breakers can be designed to respond to heat, the magnetic field or a combination of both.

For more information on wiring basics, boaters can contact the ABYC or obtain a catalog from marine electrical component manufacturer Blue Sea Systems of Bellingham, Washington, by calling 360-738-8230.

From Blue Sea Systems, 3924-D Irongate Rd., Bellingham, WA 98226. Phone: 360-738-8230, Fax: 360-734-4195.

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