Circuit Breakers

Circuit breakers operate to protect an electrical current from the damage caused by short circuits or overloads. They are automatically operated electric switches that, unlike fuses, can be reset to resume normal operation. Circuit breakers come in all shapes and sizes, from a small device designed to protect household appliances to large switchgears, which protect entire cities from high voltage circuits.
A basic circuit breaker is a simple switch that is connected to an electromagnet or a bimetallic strip. With the electromagnet design, the hotwire connects the two ends of the switch. When the switch is flipped on, electricity flows through the unit. The electricity magnetizes the electromagnet, so when the current jumps to unsafe levels, the electromagnet is strong enough to pull down a metal lever which is connected to the switch linkage. The linkage then shifts and breaks the circuit, which shuts off the electricity. Similar to the electromagnet design, the bimetallic strip design has a thin strip of metal, which bends with high currents. The bend moves the linkage, which breaks the circuit. There are also circuit breakers that use an explosive charge to throw the switch when the current rises above a certain level.

There are four main types of circuit breakers: Miniature Circuit Breakers (MCB), Moulded Case Circuit Breakers (MCCB), Air Circuit Breakers, and Vacuum Circuit Breakers. MCBs have a current of no more than 100 A. They have a thermal or thermal magnetic operation. MCCBs have a current of up to 1000 A. They also have a thermal or thermal magnetic operation. Air Circuit Breakers have a current of up to 10,000 A. They are either electronically controlled or microprocessor controlled and are often used for main power distribution in large industrial plants. Vacuum Circuit Breakers have a current of up to 3000 A. They have longer life expectancies than air circuit breakers.