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, causing death or serious injury. A safety switch detects the loss of 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.