Circuit breakers

Circuit breakers are also used to protect appliances and electrical circuits. A circuit breaker is composed of a spring-loaded push switch, a spring-loaded soft iron bolt and an electromagnet. If the current is too high the circuit breaker switches to ‘off’, breaking the flow of current. It’s more convenient than a fuse because you can simply switch it back on again. A fuse, on the other hand, needs to be replaced.

A residual current circuit breaker (RCCB) is able to protect some circuits. They work by detecting what the difference is between the neutral wire and the live wire. One of their main advantages is that they’re able to react much faster than a fuse.

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Earthing

The role of the earth wire is to form a save route for a current to flow through in case the live wire should move and touch the casing. Most electrical appliances, like fridges and cookers, are contained within a metal case so if this was to happen and there was no earth wire you’d get an electric shock if you touched the metal.

Instead, the current goes through the earth wire via the earth terminal which is connected to the metal casing. As the earth wire has a very low resistance the current flowing through it increases, causing the fuse to break and the appliance to disconnect.

Not all appliances contain earth wires. Appliances like vacuum cleaners consist of a plastic casing instead. Others have been created so that it’s not possible for the casing to come into contact with the live wire. This means that even if the wires were to come loose you wouldn’t get an electric shock from touching the appliance. This is known as double insulation. You can tell if an appliance has double insulation by the symbol below.