RCD, RCBO and RCCB explained for buyers: Type AC vs Type A, 30 mA vs 100 mA/300 mA, pole configurations, and when to specify an RCBO instead of an RCD plus MCB.
Residual-current devices are the protection that trips on current leaking to earth rather than on overcurrent, and they are the part most often specified wrong because the names — RCD, RCBO, RCCB, ELCB, GFCI — overlap while the standards use different letters. This guide sets out what each one does, the choices that actually change the part number, and what to put on a purchase order.
All of these devices compare the current leaving a circuit with the current returning. If the difference — the "residual current" — exceeds the rating, they open. What differs is the sensing type, whether they also break overcurrent, and how many poles they switch.
| Device | Breaks overcurrent? | Typical use |
|---|---|---|
| RCCB / RCD (residual-current only) | No | Pure earth-leakage protection, paired with an MCB or fuse |
| RCBO (residual + overcurrent) | Yes | Combined earth-leakage and overcurrent in one module-wide device |
| ELCB (older voltage-operated) | No | Legacy installations; largely superseded by RCCB |
| GFCI (North American term) | Varies | US/Canada receptacle or breaker form |
An RCCB (often just called an RCD) only senses earth leakage. It must sit behind an MCB or fuse that handles overload and short circuit, and it needs its own pole(s). An RCBO does both jobs in a single, usually one- or two-module-wide device. For a new consumer unit or panel where space and per-circuit isolation matter, RCBO per circuit is common; for a main incomer or a retrofit where you only want to add earth-leakage protection to an existing board, an RCCB ahead of the existing breakers is simpler.
The trade-off is cost and selectivity: a single RCCB protects many circuits, but any leakage on any of them trips the whole group; RCBOs localise the fault to one circuit. Specify RCBO when you cannot tolerate a whole-board trip, and RCCB when you want one device protecting a group and accept the group trip.
The type states which leakage waveforms the device will detect.
| Type | Detects | Where required |
|---|---|---|
| AC | 50/60 Hz sinusoidal AC leakage only | Legacy resistive loads; increasingly not accepted |
| A | AC plus pulsating DC (half-wave rectified) | Modern equipment, drives, LED drivers, EV, appliances |
| F | A plus higher-frequency AC and mixed frequencies | VFDs, dimmers, complex electronic loads |
For almost any panel feeding modern electronics, Type A is the minimum to specify; Type AC will miss the DC-component leakage that today's drives and power supplies produce, so the protection may not operate as expected. Confirm Type A unless you have a documented reason for AC, and use Type F where variable-frequency drives or dimmers are present.
The rating is the residual current at which the device trips. 30 mA is the value for personal protection — the threshold below which a shock is unlikely to be fatal, and the usual requirement for sockets and final circuits in dwellings, bathrooms, outdoor and construction supplies. 100 mA and 300 mA are for fire protection and for the upstream device in a selective (time-delayed) arrangement, where a downstream 30 mA device must trip first.
Two rules: do not put 30 mA where a standing leak (large IT loads, long cable runs) will cause nuisance tripping — use 100 mA or 300 mA for that group and keep 30 mA for the final circuits; and where two devices are in series, the upstream one must be time-delayed (S-type) so the downstream one clears first.
Residual-current devices come in 2-pole (single-phase, switches line and neutral) and 4-pole (three-phase plus neutral). For single-phase supplies use 1P+N or 2P; for three-phase use 3P+N or 4P. Switching the neutral matters: if neutral is not interrupted, a fault can leave a live-neutral loop that defeats the protection. State the pole count on the order, and confirm the device is approved for the supply system (TN-C-S, TT, TN-S) you are installing into.
ELEHPD supplies RCBO, RCCB/RCD, ELCB and GFCI devices in Type A and Type AC, 30/100/300 mA, 1P+N through 4P, with the matching MCBs and distribution boards for a complete earth-leakage protection scheme.
Send the ratings, dimensions and quantities you are working to and we will confirm the closest match from the ELEHPD catalogue, the compliance documents available for it and the lead time. OEM branding, private model numbering and buyer-specific cartons are available on qualified volumes.