What is a Circuit Breaker

A circuit breaker as the name says is a device which is used to protect the circuit from damage caused by an overload or short circuit. It is an automatically operated electrical switch designed to protect an electrical circuit. A circuit breaker is often confused with a FUSE, which is a different device altogether as fuse only operates ONCE and then it has to be replaced. The circuit breaker was invented in 1836 by an American, Charles Grafton Page later implemented by THOMAS A EDISON in 1879 and later by Hugo Stotz.


They like a fuse have a definite LIMIT of the capacity of the current they can carry, when their LIMIT is breached the circuit breaker BREAKS the connection of the circuit i.e. the flow of current is stopped. The basic parts of a circuit breaker are the switch and a moving, conductive contact plate that moves the switch when electricity comes into contact with it. In the circuit box the contact plate is connected to a stationary plate that allows electricity to flow, but if the circuit is overloaded the contact plate will force the switch to flip and break the electrical flow.

Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit, some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker.

The main types of circuit breaker are as follows:-

  • Magnetic Type Circuit Breaker:
    A magnetic circuit breaker uses electromagnetism to break the circuit. A SOLENOID is used in some designs, the more the current the more will be its pulling force. When excess of current is passed through these MAGNETIC type circuit breakers, the electromagnetic force acting upon the circuit also becomes stronger. When the electrical load exceeds the prescribed capacity, the electromagnetic force will be powerful enough to force the circuit breaker lever down and move the contact plate which flips the switch.
  • Thermal Circuit Breakers:
    As the name indicates, these type of circuit breakers use HEAT to break the circuit. Thermal circuit breakers can be found in most distribution boards. Thermal circuit breaker contains a Bi-Metallic strip i.e. two types of metal on each side. Each type of metal expands differently to bend the strip. When the electricity is too strong then the strip is bent at an angle which will turn over the contact plate and break the circuit.
    The third type combines the two i.e. uses electromagnetism as well as HEAT. This device has an electromagnet that protects against sudden surges in the electrical load and a bimetallic strip that protects against prolonged electrical overload and overheating.

Some other types of circuit breakers are: Common trip breakers, medium voltage circuit breakers, high voltage circuit breakers, Sulphur hexafluoride (SF6) high-voltage circuit-breakers.