Circuit Breakers

A circuit breaker is any electrical device that protects, or breaks, a circuit under a particular set of overcurrent conditions. An industrial or commercial fuse is one type of circuit breaker. A fuse uses a calibrated current-carrying element to control the current passing through the system. If the current applied to the fuse generates enough heat to exceed the melting point of the fuse element, the fuse will open, or break, the circuit.

In the power electronics industry, "circuit breaker" also has become the accepted term for an electromechanical device that uses a moving switch (rather than a melting element) to divert an overcurrent condition from the electrical circuit path. Using this definition, circuit breakers differ from the simple fuse by virtue of their re-usability. A simple fuse needs to be replaced after each overcurrent situation; a circuit breaker simply needs to be reset.

Circuit Breaker Triggers

The switch in an electromechanical circuit breaker can be triggered by one of two methods:

  • Electromagnet - electricity flowing through the circuit magnetizes the switch; if the current exceeds the recommended level, the magnetic force created is sufficient to pull the switch to the linkage and break the circuit
  • Bi-Metallic Strip - same principle as the electromagnetic version; if the current exceed the recommended level, the generated heat causes the strip to bend or deform to pull the switch out of the circuit path

Circuit Breaker Performance

The conventional circuit breaker's performance is limited by:

  • Slow response time of bi-metal current sensors.
  • Mechanical tolerances that affect both the thermal and the magnetic trip limits.
  • Inability to differentiate between arcing and normal start up transients caused by large motors or incandescent lamps.
  • The necessity to set the magnetic trip threshold high enough to prevent nuisance tripping

Advances in the electronics industry have led to the development of Semiconductor Circuit Breakers to combat these limitations. Semiconductor circuit breakers monitor the current flowing through a circuit digitally. These types of circuit breakers trip a true electrical switch (no moving parts) when the registered value exceeds a given point. Semiconductors are much more precise, but much more expensive than electromechanical circuit breakers. They are typically seen in industrial and commercial applications rather than residential circuit protection designs. Like other styles of circuit breakers, semiconductor circuit breakers can be reset for continued use.

Find and Buy Circuit Breakers at National Fuse Products

National Fuse carries a wide variety of both conventional and semiconductor style circuit breakers to meet your circuit protection needs. We specialize in obsolete or hard-to-find replacement circuit breakers for industrial and commercial applications. We also handle most of the latest molded-case circuit breaker designs from the leading North American, European, and Japanese manufacturers.