Switch on ‘safety’ measures
A safety switch is an electrical safety device which is specially designed to immediately switch off the electricity when electricity ‘leaks’ to earth at a level harmful to human. This device offers a high level of personal protection from shock.
Safety switch is general name for a residential current device (RCD) or earth leakage circuit breaker (ELCB). These work on the principle of ‘what goes in must come out’. They operate by continuously comparing the current flow in both Active (supply) and Neutral (return) Conductors of Electrical Circuit. If some of the current in the Active Conductor is not returning through the neutral conductor it is leaking to earth.
Safety switch typically operate within 10 to 50 milli-seconds and disconnects the electric supply when they sense harmful leakage current, usually 30 milliamps. The sensitivity and speed of disconnection are such that any earth leakage current will be immediately detected and automatically switched off before it can cause injury or damage.
Electrical accidents usually show contact between ‘live’ parts and earth as the predominant shock path. Contact with live parts may occur by touching bare conductor, internal appliance parts or external appliance parts that have become live because of an internal fault. Contact with earth occurs through normal body contact with the ground or earthed metal parts. Damp areas such as bathrooms, pools etc, increase the risk and severity of electricity shock as water conducts electricity.Miniature Circuit Breakers (MCB) and fuses provide equipment or installation protection and operate in response to an electrical overload or short circuit when high fault currents flow. Short circuit flow to earth via your installation’s earthing system causes either the MCB to trip or blow up the fuse, disconnecting the electricity from the fault circuit.
However, if the electrical resistance in the earth fault current path is too high to allow the MCB to trip or fuse to blow, then electricity can continue to flow to earth for an extended time, creating dangerous voltages and currents. Safety switches (with or without over current device) can detect a very low level of electricity flowing to earth and immediately switch the electricity off. Safety switches have another important advantage.
They reduce the risk of fire by detecting electrical leakages to earth in wiring and accessories. On a circuit protected by a Safety switch, if a fault cause electricity to flow through a person’s body, the Safety switch will automatically disconnect the electric supply avoiding the risk of serious injury or death.
Two or more Safety switches are now mandatory in all new and old houses for all power and lighting circuits. It is recommended that electrical installations be designed in such a way that some lighting and power point circuit are protected by one Safety switch and the rest by another one.Circuit Breakers and Safety Switches look similar as they both feature a large on/off switch. However, a Safety Switch has a test button labelled ‘Press to Test’. Once a Safety Switch has been installed you are far less likely to receive a serious electric shock. However, do not become complacent and take risks just because you have a Safety Switch installed. Test the switch at least once a month by pressing the test button.
N.A. LOKESH KUMAR
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