Low-Voltage Air Circuit Breakers:

A low-voltage circuit breaker is one that is suited for circuits rated at 600 volts or lower. One of the most generally used low-voltage air circuit breakers is the molded case circuit breaker that was show in the figure.

Figure: Molded Case Circuit Breaker

A cutaway display of the molded case circuit breaker is display in above figure.

Figure: Cutaway View of Molded Case Circuit Breaker

A circuit could be connected or disconnected using a circuit breaker through manually moving the operating handle to the ON or OFF position.  All breakers, along with the exception of extremely small ones, have a linkage among the operating handle and contacts which permit a quick make (quick break contact action) regardless of how fast the operating handle is moved. The handle is also designed so which it cannot be held shut on a short circuit or overloads condition. The handle will go to the trip-free position if the circuit breaker opens under one of these conditions. The trip-free position is midway among the ON and OFF positions and cannot be re-shut until the handle is pushed to the OFF position and reset.