What is the purpose of an earth wire in mains circuits?

The purpose of an earth wire in mains circuits is to provide a safe route for electric current to flow if a fault occurs.

In more detail, the earth wire is a crucial safety feature in electrical systems. It is typically coloured green and yellow and is connected to the metal casing of an appliance. The primary function of the earth wire is to prevent electric shocks and fires by providing a pathway for electric current to flow into the ground if there is a fault in the appliance.

For instance, if the live wire inside an appliance such as a toaster or a washing machine comes into contact with the metal casing due to a fault, the casing can become live. This can be extremely dangerous as anyone touching the appliance could receive a severe electric shock. However, if the appliance is earthed, the current will flow through the earth wire instead of passing through a person. This surge of current will trigger the circuit breaker or fuse in the consumer unit to disconnect the appliance, thereby preventing potential harm.

The earth wire is also essential in preventing electrical fires. If a fault causes an excessive amount of current to flow through the circuit, the heat generated can ignite nearby materials and start a fire. But with an earth wire in place, this excessive current is safely directed into the ground, reducing the risk of fire.

In summary, the earth wire plays a vital role in maintaining the safety of electrical appliances and systems. It provides a safe route for electric current to flow into the ground in the event of a fault, protecting users from electric shocks and preventing fires.