An RCBO provides protection against which conditions?

• A. Residual current only
• B. Overcurrent only
• C. Both residual current and overcurrent
• D. None

Answer: (C)

An RCBO combines two protective functions in one device: residual-current protection and overcurrent protection. It monitors the current in the live and neutral conductors and trips if there is an imbalance, which indicates leakage to earth and could pose a shock risk. It also trips if the current exceeding the device’s rating appears, protecting against overloads and short circuits that could overheat wires or start fires. Because it covers both scenarios, it provides protection against both residual current and overcurrent. A device that only handles residual current wouldn't trip on a high fault current, and a device that only handles overcurrent wouldn’t detect small earth faults, so the RCBO offers the most complete protection.