Residual Current Circuit Breaker

A Residual Current Circuit Breaker (RCCB), more commonly known as a Residual Current Device (RCD), helps keep people from getting electric shocks when sorting out electrical problems. The easiest way to think of an RCD is to remember that a normal circuit breaker protects property, while an RCD protects people. When an electrical fault occurs, the RCD detects that some of the current is going where it's not supposed to go and is creating a shock hazard. When this occurs, the RCD trips, preventing the flow of electricity, and offering pro­tection against electric shocks in one-fortieth of a second - a short enough periods that most healthy people aren't injured. All RCD sockets have test buttons. Modern consumer units have an integral RCD which protects all the power circuits wired through it.

A residual current circuit breaker (RCCB) has a different action. It switches off the mains supply to an appliance when it detects a leakage of current to earth or to another circuit. For example, an exposed metal part of an appliance (such as its case, or a control knob) may become live because of faulty insulation. A person touching that part conducts current to earth and receives a shock. The RCCB measures the current flowing along the live wire and that flowing along the neutral wire. Because some of the current is leaking away (through the person) the live and neutral currents are unequal. The RCCB detects this slate and switches off the supply. A typical RCCB detects a current leak as small as 30 mA, and switches off within 20 ms. This greatly reduces the chances of serious electric shock. RCCBs do not switch off if the leakage is direct from live to neutral. This is because the currents are equal. A person accidentally touching both live and neutral wires and terminals at the same time receives a shock

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