RCD, RCBO and SPD selection for a V2L board

Answer first — what a V2L board actually needs

At each EV connection point you need at least a Type A RCD, plus protection against smooth DC residual current. The DC protection comes one of two ways: a Type B RCD, or a Type A/F RCD combined with a residual-direct-current detecting device (an RDC-DD to BS IEC 62955). The most common arrangement is a Type A RCD with an RDC-DD. A plain Type AC RCD — still the default in many older boards — is not enough, because a power-electronic source can produce residual currents it may not clear.

Why a plain Type AC RCD is not enough

A Type AC RCD only responds to sinusoidal AC residual current. The power electronics in a V2L source — and in EV chargers generally — can produce residual currents with a DC component or higher-frequency content. A small smooth DC residual current can magnetically bias an AC- or A-type RCD's core and *desensitise* it, so it no longer trips at its rated residual current. That is the whole reason §722 calls for both a minimum Type A RCD and a specific means of dealing with smooth DC.

The smooth DC requirement — two compliant routes

BS 7671 gives you a choice for the smooth-DC protection, and the device standards back each route. Either device is acceptable; the difference is cost, availability and how the rest of the board is built.

• Type A RCD + RDC-DD (BS IEC 62955) — the common case. The RDC-DD detects smooth DC residual current below the level that would desensitise the upstream Type A (or Type F) RCD. If the EVSE or V2L equipment embeds this detection, an upstream Type A/F RCD is acceptable instead of a full Type B.
• Type B RCD — a single device that itself responds to higher-frequency residual currents plus smooth DC. The fallback where smooth DC detection is not otherwise provided. Typically more expensive than a Type A + RDC-DD pairing.

Where Type F fits

Type F sits between Type A and Type B. It handles the mixed-frequency residual currents a single-phase inverter or variable-speed drive can produce — exactly the kind of output a single-phase V2L source delivers — and a limited smooth DC component. It does not cover the full smooth-DC range of a Type B, so where it is used the smooth DC duty is still met by an RDC-DD. The Type F and Type B construction requirements live in BS EN 62423.

RCD or RCBO — which housing?

The type (AC / A / F / B) is the safety-load-bearing choice. The housing is a separate decision: an RCCB (to BS EN 61008-1) provides residual-current protection only and must be paired with separate overcurrent protection, while an RCBO (to BS EN 61009-1) combines residual-current and overcurrent protection in one device — common on modern V2L/backup boards so each final circuit has its own protection. Whichever housing you use, the type still matters on any EV/inverter circuit: an RCBO can be Type AC, A, F or B, and only A/F/B (with the smooth DC provision) is acceptable here.

Overcurrent — the V2L fault current is not the grid's

Overcurrent protection (MCB or the overcurrent element of an RCBO, to BS EN 60898-1) sets the trip curve (B/C/D) and breaking capacity. The trap with V2L is that a vehicle inverter delivers a much lower prospective fault current than the grid. A breaker that clears a fault quickly on a 230 V grid supply may not see enough fault current from the V2L source to operate in the required disconnection time — so automatic disconnection of supply (ADS) can fail in V2L mode even though it passes in grid mode. The product standard is only the device rating; the disconnection has to be proven by a competent person for the V2L source, not assumed from the grid figures.

Surge protection (SPD) — a separate assessment

Overvoltage surge protective devices (SPDs) protect against transient overvoltages — lightning and switching surges — and are a different question from residual-current and overcurrent protection. Whether an SPD is required is a risk assessment under the BS 7671 overvoltage provisions (broadly §443 for the requirement and §534 for selection and erection), driven by the consequences of an overvoltage at that installation, not by the presence of V2L as such. Treat it as its own line item in the design; it is not part of the RCD/RCBO type choice.

Product standards rate the device — BS 7671 governs the design

The construction-and-test standards (BS EN 61008-1, BS EN 61009-1, BS EN 62423, BS EN 60898-1, BS IEC 62955) tell you a device is built and rated correctly. They do not tell you whether your selection is correct for this installation — that is the job of BS 7671 §722 and the competent person's design and test. A device that conforms to its product standard is necessary but not sufficient; the selection, coordination and disconnection proof are the design.