On a normal power circuit, the current flowing to an appliance returns through the neutral wire. If the circuit is compromised, the electricity can leak to earth through a person in contact with the appliance or a problem with the appliance, causing death or serious injury.
A safety switch detects the difference in power from the circuit, and cuts the supply of electricity in as little as 30 milliseconds – 0.003 seconds. Importantly, this response time is faster than the critical section of a heartbeat, and therefore significantly reduces the risk of death or serious injury.
For more information or help on safety switches