A Type B RCD (Residual Current Device) protects an EV charging circuit from DC residual current — required by UK BS 7671 18th Edition wiring regulations on every domestic and commercial EV charging install. Most modern wallboxes have Type B protection built in. The ones that don't, need a separate Type B RCD in the consumer unit.
Why Type B specifically
Standard household RCDs are Type A or Type AC — they detect AC residual current (and pulsed DC, in Type A's case) and trip on imbalance. EV chargers can produce smooth DC residual current that Type A and Type AC RCDs cannot detect. If undetected, smooth DC current saturates an RCD's transformer core and can disable downstream protection — creating a shock hazard.
Type B RCDs include additional sensing for smooth DC current, providing complete protection for EV charging circuits. UK regulation BS 7671 (18th Edition) Amendment 2 explicitly requires Type B (or equivalent additional protection) on EV charging circuits for this reason.
Built-in vs separate Type B
Many modern UK wallboxes include Type B RCD protection built into the unit:
- Built-in Type B: Project EV Pro Earth, Easee One, Sync EV, MyEnergi Zappi v2.2, Andersen A2, Hypervolt Home 3 Pro.
- Requires separate Type B: some Pod Point models, Rolec EVHP, older Ohme Home variants. Check the install datasheet.
Built-in saves £80-150 in install bill of materials. If your wallbox has built-in Type B, you don't need to buy this product. If it doesn't, you do.
Specifications
UK domestic Type B RCDs are typically:
- 32A rated — sized for typical 7kW (32A single-phase) wallbox.
- 40A or 63A for three-phase or larger commercial installs.
- 30mA trip threshold — UK domestic standard for personal protection.
- DIN-rail mount — fits standard UK consumer units.
Brands we stock
- MK Electric — UK-made, the highest-volume premium domestic RCBO/RCD brand. Direct compatibility with most UK consumer units (Hager, Wylex, Crabtree).
- Hager — German-engineered, cost-effective, native fit in Hager consumer units.
- Wylex — UK volume brand, native fit in Wylex consumer units.
- Schneider Electric — premium German engineering, used in commercial and high-end domestic.
RCBO alternative
An RCBO combines an MCB and RCD in a single DIN-rail device — the cleanest way to protect an EV circuit if you have only one or two free DIN slots. See our RCBO range for combined-protection options.
Installation
Type B RCD installs in the consumer unit (fuse box) on the dedicated EV charging circuit, typically between the main isolator and the EV breaker. Installation is regulated under the Electricity at Work Regulations 1989 and must be done by a qualified electrician. Self-install is unsafe and breaches Building Regulations.
Every wallbox install we arrange includes the appropriate RCD where required, fitted by an OZEV-approved electrician.
Three-phase
For three-phase EV installs (22kW wallboxes), you need a three-phase Type B RCD or equivalent. These are sold as four-pole devices (3 phases + neutral). See three-phase listings in this collection for the right product.
What it doesn't do
A Type B RCD doesn't replace overcurrent protection (the MCB / fuse). It protects against earth leakage, not over-current. Both are required — typically as separate MCB + RCD, or combined in a single RCBO.