How would you decide between using an RCCB, an RCBO, or both on a circuit?

• A. Use RCBO for all circuits always
• B. Use RCCB for overcurrent protection only
• C. Use RCCB for earth-leakage protection alone; use RCBO when both leakage protection and overcurrent protection are required in one device
• D. Use RCCB for earth leakage and short circuit protection

Answer: (C)

The main idea is understanding what each device protects against. An RCCB (RCD) detects earth-leakage by comparing current in the live and neutral conductors and trips if there’s an imbalance. It provides earth-leakage protection, but it does not handle overcurrent protection, so it won’t automatically disconnect a circuit during a short circuit or overload unless you also have a separate overcurrent device.

An RCBO combines both functions in one unit: it trips for earth leakage like an RCCB and also trips on overcurrent (short circuit or overload) like a circuit breaker. So you’d choose an RCBO when you need both protections for a circuit and prefer a single device.

If you only need protection against earth leakage, an RCCB is appropriate. If you need both leakage protection and overcurrent protection in one device, an RCBO is the better choice. Using an RCCB thinking it will protect against short circuits isn’t correct, since it won’t provide overcurrent protection; you’d need a separate MCB or an RCBO for that. In practice, you could put an RCCB with a separate MCB, but that isn’t as integrated as using an RCBO.