What is an RCCB?

RCCB stands for Residual Current Circuit Breaker. Other names for the same device are RCD, Residual Current Device and GFCI, Ground Fault Circuit Interrupter. Earlier device used for a similar function was ELCB or Earth Leakage Circuit Breaker. RCCB is an electrical safety device which interrupts the electrical circuit when the current passing through the conductor is not equal and opposite in both directions. Imbalance indicates improper current flow like an earth leakage current or current flowing to another powered conductor. RCCB is meant to reduce the severity of injury caused by an electric shock. The victim may still fall due to the shock and sustain injury before the circuit is interrupted by the device. Another caveat mentioned for the RCCB is that it offers no protection when a person touches both conductors at the same time.

RCCB looks for unbalanced current between the supply and return conductors of the protected circuit. Any difference between the currents in these conductors is taken as leakage current and has a shock hazard. The conductors are quickly disconnected (tripped) by the RCCB to reduce the injury to the human being in contact. It is mentioned that an alternating current of more than 20 mA can cause serious injury within a fraction of a second. RCCBs typically disconnect the circuit within 25 to 40 milliseconds of detection of a leakage current. They operate by measuring the current balance between the conductors using a differential current transformer. The differential current transformer measures the difference between current flowing through the live conductor and the neutral conductor which returns the current to the source. If there is a difference, it is taken as leakage to earth or ground or to another circuit and RCCB will open its contacts.

RCCB works even if the earth connection of the installation is damaged or incomplete. In case of three phase connections, all three live conductors and the neutral should pass through the current transformer. You can see ports for the three live conductors (incoming and outgoing) for the RCCB devices illustrated in the video clips. Test button is there to check the proper function of the device after installation. While trying to fix the devices in old installations, if there is already leakage currents in the wiring, the circuit will not power on until the sources of leakage are identified and rectified!