Which protective device provides both overcurrent protection and residual current protection in one unit?

• A. MCB
• B. RCD
• C. RCBO
• D. FUSE

Answer: (C)

An RCBO combines two protective roles in one unit: residual current protection and overcurrent protection. It acts as an RCD by monitoring the difference between live and neutral currents and tripping if there’s leakage to earth, which helps prevent electric shock. At the same time, it includes a circuit-breaker function (like an MCB) that trips on overcurrent or short circuits to protect the wiring from overheating.

This means it provides both protections in a single device. A standalone MCB protects only against overcurrent, a standalone RCD protects only against earth leakage, and a fuse protects against overcurrent but isn’t resettable and doesn’t provide residual-current protection.