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. 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. 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. From Blue Sea Systems, 3924-D Irongate Rd., Bellingham, WA 98226. Scott Renne is president of Blue Sea Systems, which produces fuses, breakers, breaker panels, meters, switches, connectors and many other top quality marine electrical components.