Which option correctly describes the function of an RCBO?

• A. An RCBO provides residual current and overcurrent protection in one device.
• B. An RCBO is a lighting control device only.
• C. An RCBO is a surge protector for telecom lines.
• D. An RCBO is a thermal fuse for cables.

Answer: (C)

An RCBO provides two protective functions in one device: residual-current protection and overcurrent protection. It combines the job of an RCD, which detects leakage to earth by monitoring the balance between live and neutral conductors, with the job of an MCB, which trips when current overloads or short circuits occur. If there’s a fault causing current to leak to earth (for example, a faulted appliance or contact with a live part), the RCBO detects the imbalance and trips to prevent electric shock. If the circuit draws too much current, it trips to prevent overheating of conductors or damage. Having both protections in a single unit simplifies installation and reduces nuisance trips compared with using separate devices. This isn't a surge protector for telecom lines, a lighting control device, or a thermal fuse for cables, which serve different purposes.