The Residual Current Circuit Breaker or RCCB is an electrical protective device that gives protection against earth fault or ground fault or earth leakage. An RCCB can give protection against electrical shock. Earth fault or earth leakage fault in a power system can cause excess heating, more power consumption, unhealthy system, burning or fire, etc. So, the protection against earth leakage is very important. RCCB is the device that can sense the leakage current in the power system and can interrupt the circuit.

RCCB Construction

Here, you can see the constructional diagram of a Residual Current Circuit Breaker or RCCB.

The main element of the RCCB is the Core consisting of three coils. One coil is to be connected in the series with the phase, another coil is to be connected in series with the neutral. And the sensing coil is connected to the relay. The relay used in the RCCB is a current sensing relay. The main function of the relay is to actuate or send the signal to the circuit breaker contacts when a leakage current arises in the circuit.

Also, you can see the RCCB has a Test button series with a current limiting resistor. The function of this switch is when it is pressed the current will flow through the coil connected with neutral only. As the switch makes a closed path between phase and neutral directly, so there will be a very high current flow in the circuit. The current limiting resistor limits that high current to flow in the circuit. So, the test button comes in the use to test the operation of the RCCB, is it working normally or not. Also, remember that the no of turns in both coils connected in series with phase and neutral are the same. So, when an equal current flows in the circuit, they will produce the same amount of magnetic flux. The both coils are wound in the opposite direction to each other.

RCCB Working Principle

The working principle of the RCCB is very simple. When there is no fault in the circuit, the phase and neutral will carry an equal current. As the equal current flows in both phase and neutral coil, they will produce the same amount of magnetic flux and as they are wound in the opposite direction to each other, the resultant magnetic flux will be zero. As the resultant flux is zero, there will be no current flow in the sensing coil or to the relay.

When earth leakage or earth fault occurs, the current will start flowing from the phase to the ground. So, an unbalanced current starts flowing through the phase and neutral. As, the unbalance current flows, the magnetic flux produced by the phase and neutral coil also be unequal. So a resultant flux will produce which cause to produce an emf in the sensing coil. As the sensing coil is in a closed circuit with the relay, a current will start flowing through the sensing coil and relay. The relay will send a signal to the circuit breaker to break the contact to disconnect the power supply or trip the RCCB.

RCCB Function

The main function of an RCCB is to give protection against leakage current fault. It trips or turned off the power supply when a leakage current fault such as earth leakage, electric shock, etc occurs. Remember that an RCCB can not give protection against Short Circuit and Overload Fault. The RCCB can sense leakage current only, it can not sense the high current flow or short circuit current. So, an MCB is always used with an RCCB. If the high current causes to flow a unbalance current in the circuit then the RCCB will trip but if the current flow is balanced or equal in both incoming and outgoing line then it will not trip however the high current flows. For, example when a short circuit fault occurs, a very high current flows but equal, so in this case the RCCB cannot give protection even it may damage due to high current flow.

Application and Uses of RCCB

1. RCCB is used in domestic as well as industrial wiring for the protection of electrical shock.

2. RCCB is used for the protection against earth leakage fault.

3. RCCB used in Home, Offices, building to prevent electrical shock as well as leakage current fault protection. Generally, 30mA sensing current RCCBs are used to prevent electrical shock.

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Residual Current Circuit Breaker(RCCB), Working, Function, Use Reviewed by Author on November 03, 2021 Rating: 5