Which device provides residual current protection (earth fault protection) in electrical installations?

• A. MCB
• B. RCBO
• C. Bonding device
• D. RCCB

Answer: (D)

Residual current protection works by watching the current in the live and neutral conductors and tripping the supply when there’s an imbalance, which indicates leakage to earth. The device designed for this function is the RCCB. It continuously compares the currents in and out; if some current escapes to earth (for example through a person), the imbalance is detected and the circuit is cut off quickly to reduce the risk of electric shock or fire.

While RCBOs also provide earth fault protection, they combine it with overcurrent protection and are used when both leakage protection and overcurrent protection are needed. MCBs protect against overcurrent only, and bonding devices are for establishing equipotential bonding rather than interrupting the circuit. So for strictly residual current (earth fault) protection, RCCB is the appropriate device.