RCBOs — Residual Current Breaker with Overcurrent — combine an MCB and an RCD into a single DIN-rail device. The cleanest, most space-efficient way to protect a domestic EV charging circuit under BS 7671 18th Edition. Sized 32A or 40A for typical 7-22kW wallbox installs, with Type B residual current sensing required for EV-specific use.
What an RCBO does
An RCBO performs two functions in a single device:
- MCB (Miniature Circuit Breaker) — over-current protection. Trips when current exceeds the rated value (e.g. 32A) for too long.
- RCD (Residual Current Device) — earth-leakage protection. Trips when there's an imbalance between live and neutral (indicating leakage to earth, typically through a person).
Standalone MCBs and RCDs each take one DIN slot in the consumer unit. An RCBO does both jobs in one slot — saves space, simplifies wiring, and is the modern UK standard for new installs.
Why Type B sensing is required for EV
EV chargers can produce smooth DC residual current that Type A and AC RCDs cannot detect — leaving downstream protection compromised. UK BS 7671 18th Edition Amendment 2 requires Type B residual current sensing on EV charging circuits. So you need either:
- A Type B RCBO directly (combined MCB + Type B RCD).
- A Type A RCBO + separate Type B RCD downstream.
- A wallbox with built-in Type B protection — see our Type B RCD range for the standalone product.
Many modern wallboxes (Project EV Pro Earth, Easee One, Andersen A2, Hypervolt Home 3) have built-in Type B protection — meaning a Type A RCBO upstream is sufficient. Saves on RCD purchase. Always check the wallbox's install datasheet to confirm which protection is required upstream.
Sizing — 32A or 40A?
For domestic EV use:
- 32A single-phase — for 7.4kW wallboxes. The mainstream UK domestic spec.
- 40A single-phase — slight headroom; useful if your home electrician wants buffer for inrush currents.
- 16A three-phase (3P+N) — for 11kW three-phase wallboxes.
- 32A three-phase (3P+N) — for 22kW three-phase wallboxes.
Trip threshold — 30mA
UK domestic standard for personal protection is 30mA — trips on 30 milliamps of leakage, fast enough to prevent fatal shock. Industrial / commercial sometimes uses 100mA or 300mA for circuit protection (not personal protection); these are not appropriate for EV charging.
Brands we stock
- MK Electric — UK-made, native fit in MK Sentry consumer units. The premium domestic choice.
- Hager — German-engineered, native fit in Hager consumer units.
- Wylex — UK volume brand, native fit in Wylex consumer units.
- Schneider Electric — premium, used in commercial and high-end domestic.
Match the RCBO brand to your existing consumer unit's manufacturer. Different brands have different DIN-rail dimensions and busbar arrangements; mixing is electrically fine but mechanically awkward.
RCBO vs separate MCB + RCD
RCBO advantages:
- Single device — one DIN slot, simpler wiring.
- Per-circuit protection — if the RCD trips on the EV circuit, only the EV circuit goes off (not the whole consumer unit's downstream loads, as with a single shared RCD).
- Easier identification of fault location (no need to pin down which circuit triggered the trip).
Standalone MCB + RCD advantages:
- Cheaper per-installation if you have multiple RCD-protected circuits sharing a single RCD.
- Older consumer units may only support standalone, not RCBO.
For a new EV install, RCBO is almost always the right answer.
Installation
RCBO install requires a qualified electrician working to BS 7671 18th Edition. Self-install is unsafe and breaches the Electricity at Work Regulations 1989. Every wallbox install we arrange includes the appropriate RCBO where required.
What we stock
- 32A and 40A Type A and Type B RCBOs in MK, Hager, Wylex, Schneider.
- Three-phase 16A and 32A 4P (3P+N) RCBOs.
- Compatible busbars and DIN-rail accessories.