OHS practices - Hazards

Safety switches

Residual current devices (RCDs) are often known as safety switches. An RCD is an electrical safety device specially designed to immediately switch the electricity off when electricity leaking to earth is detected at a level harmful to a person using electrical equipment.

A residual current device.

 

An RCD offers a high level of personal protection from electric shock.
The current entering a piece of equipment and leaving a piece of equipment should always be the same. If there is any difference this is known as earth leakage. This is measured at the RCD and will disconnect the electrical supply should this occur.

RCDs are designed to disconnect the electrical supply within 10 to 50 milliseconds when they sense harmful leakage, typically 30 milliamps.

RCDs have saved many lives since they have been made compulsory on all power circuits in domestic houses since 2000.

Earth leakage can occur when a person comes in contact with something that has no insulation on it but has electricity running through it. This is referred to as a live part.

Contact with live parts may occur by touching:

•  bare conductors
• internal parts of an appliance
• external parts of an appliance that have become live because of an internal fault.

Contact with earth occurs through normal body contact with the ground or earthed metal parts.