What is an RCD?
An RCD is a safety device that disconnects a circuit when it detects an imbalance of the electric current. It works on the principle that the electricity flowing into a circuit must be equal to the current flowing out of a circuit. When a person receives a shock, it means some current is diverted through the body directly to earth.
If the RCD detects an imbalance in the electrical current, indicating a leakage to earth, it immediately cuts the electricity supply to prevent electrocution.
An RCD cannot detect all types of faults, for example if a person receives a shock between the active and neutral conductors. However, these circumstances are rare and the vast majority of incidents occur between the active conductor and earth, which is protected by an RCD.
If a person comes in contact with a live electrical conductor, electricity flows through their body, causing an electric shock. Effects can vary from a tingling sensation or muscular pain to breathing difficulties, burns and heart failure.
RCDs are extremely sensitive, disconnecting within 10 to 50 milliseconds of detecting a leakage current. This is usually 30 milliamps for domestic residences but may be lower in other locations such as hospitals. This stops the flow of electricity through someone’s body to earth. Importantly, this response time is much faster than the critical section of the cardiac cycle and therefore significantly reduces the risk of death or serious injury.
RCDs also protect against fire caused by faults in appliances, tools and wiring. If these faults go undetected they could cause a fire or personal injury. RCDs provide a means of early fault detection.
RCDs are required to be fitted at the meter box (main switchboard) or distribution board for the residence.
Various brands of RCDs are available; however they can all be identified by the test button located on the front of the device.
If you press the ‘test’ button, or the RCD has detected an imbalance, the on/off switch will jump to the “off” position.