Circuit Breaker Basics

A man examines a circuit breaker.
  • Intermediate

A circuit breaker is an automatic switch in an electric panel. It constantly monitors the amount of electricity flowing through the circuit. When there is a faulty situation such as an overload or short circuit, the circuit breaker immediately stops the flow of current through the circuit. This prevents damage and electric shock to nearby people and surroundings. Circuit breakers are similar to fuses, which are also devices that protect circuits from overloading. However most fuses, with the exception of renewable fuses, can be only used once. Circuit breakers can be reset and reused multiple times, and are easier to operate.

Need for Circuit Breakers

The electric supply in your home is composed of many circuits, all of which consist of a “hot node” and a “neutral node.” The hot node is the inlet or wire from which electric current is being delivered to the circuit, while the neutral node is the wire that is connected to the ground. The hot node and the neutral node are always kept separate from each other, in a properly working circuit. However, in case of an accident, these two wires may melt and fuse. In such a situation, there is no resistance in the circuit and electric charge flows freely between the nodes. Your body is a grounding point, which if connected to the hot wire can cause a strong electric current to flow through it. This is why a circuit breaker is a crucial component of electric safety in every building.

Working of Circuit Breakers

A circuit breaker consists of a switch, which when pulled down, breaks the circuit. In basic circuit breakers, the lever is pulled down using heat energy or an electromagnet.

Thermal Circuit Breakers

Some circuit breakers use heat to pull down the circuit breaker switch. A bimetallic strip is used for this purpose. The strip consists of 2 different metals, both of which have different melting points. When the electric current in the circuit exceeds the safety limit, the heat causes the bimetallic strip to bend. The bending of the strip pulls down the circuit breaker switch and opens the circuit, stopping the current flow.

Electromagnetic Circuit Breakers

In this type of circuit breaker, an electromagnet comprises the mechanism used to pull down the switch. The pulling force of the electromagnet increases with the level of current that flows through it. When the current level is higher than normal the electromagnet develops a very strong magnetic pull, which forces the circuit breaker switch down. This causes the circuit to break.

Some circuit breakers use a combination of bimetallic strip and electromagnet to provide protection from overheating. There are also several advanced versions of circuit breakers available, which are faster and more precise in the monitoring of the current level. A Ground Fault Circuit Interrupter (GFCI) is one of the examples of a more sophisticated circuit breaker. High voltage circuit breakers use sulfur hexafluoride gas, but because of its negative effects on the environment, other alternatives are being used increasingly.