Residual Current Circuit Breakers (RCD)
§531 — Residual Current Devices (RCDs)
Types
| Type | Detects | Application |
|---|---|---|
| AC | Alternating current (sinusoidal) | Obsolete, no longer permitted for new installations |
| A | Alternating current + pulsating DC | Standard for residential buildings |
| F | A + high-frequency components | Frequency inverters (single-phase) |
| B | A + pure DC | Charging stations, frequency inverters (three-phase) |
Threshold values
- 30 mA — personal protection in dwellings, bathrooms, outdoors (§411.3.3, §701, §708).
- 100 / 300 mA — fire protection in agriculture (§705), industry.
- 500 mA — distribution only, no personal protection.
NEN 1010 explicitly states: every socket outlet up to and including 32 A for general use must be protected by additional protection of maximum 30 mA — this therefore applies not only in dwellings, but to all circuits with this type of connection point, regardless of the room.
ALS or ALA — recognizing the schematic symbol
On a diagram or in a distribution board, an RCD (ALS, residual-current protection only) and an RCBO (ALA, combined residual-current + overcurrent protection in one device) can be distinguished without opening the device itself:
- RCD (ALS) — the symbol shows only the differential-current bar, without the curved S-shape/rectangle of a circuit breaker and without a B/C/D letter. The stated amp value is the rated residual current / let-through current (the maximum current the device may pass), not a thermal protection value.
- RCBO (ALA) — combines the circuit-breaker symbol (with a B/C/D letter) with the residual-current symbol in one block. Here, the amp value is indeed the rated current
Inof the integrated circuit breaker.
Do not confuse the two when reading a diagram: an RCD does not protect a cable against overload, an RCBO does.
Testing with the installation tester
An RCD is checked with an installation tester at three points, not just one:
- At I∆n (the rated tripping current) the RCD must trip within ≤ 300 ms.
- At 5 × I∆n the RCD must trip faster: ≤ 40 ms.
- At ½ × I∆n the RCD must not trip — an RCD that already trips here is set too sensitively or is defective, causing nuisance tripping.
- A selective type S RCD trips with a delay, between 130–500 ms, so that a downstream fast RCD gets the first chance to trip.
Besides this measurement with the installation tester, the manual test button (T-button) on the device itself remains a separate, simpler check — an operation that even a layperson may carry out, at least once every six months.
Practical installation
- RCD before the final circuits, after the main fuse.
- Test button at least once every six months (recommendation: quarterly).
- No shared neutral conductors between different RCD groups.
- Cumulative leakage currents must remain < 30% of I∆n; otherwise, use type B or multiple RCDs.