RCD vs RCBO: what protection does each provide?
Supports revision for: C&G 2365 Unit 203. Coverage references only; no awarding-body affiliation or qualification is conferred.
RCD is the family name for residual-current devices. An RCBO belongs to that family and also provides overcurrent protection. When someone contrasts an ‘RCD’ with an RCBO, they usually mean an RCCB: residual-current protection without built-in overload protection.
Electrical learning · BS 7671:2018+A4:2026 · Sources checked 29 October 2026
| Function | RCCB | RCBO |
|---|---|---|
| Residual current | Detects an imbalance between currents in the live conductors | Provides residual-current protection too |
| Overload and short circuit | Needs suitable overcurrent protection elsewhere | Combines residual-current and overcurrent functions |
| Reading the markings | RCD type describes the residual-current waveforms it can detect | Residual-current type and overcurrent trip curve describe different things |
A common mix-up
An RCD is not a guarantee against every electric shock, and an RCCB does not replace a fuse or circuit-breaker for overload protection. BS 7671:2018+A4:2026 Regulation 531.3.3 concerns RCD selection; the complete design still needs the other protective measures.
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Key numbers
- 30 mA
- RCD rating for additional protection, such as sockets up to 32 A (Reg 411.3.3). Not a 'safe' shock.
Common mistakes
- Thinking an RCCB protects against overload.
- Reading the B or C on an RCBO as its RCD type. It's the trip curve.
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