# Earthing & bonding fundamentals for V2L

> Every electrical source needs exactly **one** neutral-earth reference. The grid's is made for you at the substation; a **floating** V2L output has none, so a single bond must be supplied at the source side, in circuit only when on V2L — never two bonds in parallel. The protective conductor (earth) stays **continuous and is never switched**. Main and supplementary bonding tie the installation's metalwork to one potential. Which earthing arrangement you use depends on **where** the board is: a separate outbuilding is made TT with a local electrode; an indoor board keeps the single PME/MET earth and uses an isolation transformer. It must be designed and **proven by test** by a competent person, and the vehicle manufacturer does not sanction this use.

**Safety frame.** This is education, not an instruction to carry out work. Work connecting V2L equipment to fixed wiring is safety-critical and may be notifiable under Part P. It must be designed, installed, inspected and tested by a competent person to the current edition of BS 7671. Vehicle manufacturers generally do not sanction back-feeding fixed wiring from V2L outlets; follow manufacturer instructions.

## In short

- One source, one neutral-earth reference. The grid's lives at the substation; a **floating** V2L output has none until you supply one.
- Make exactly **one** bond, on the source side, in circuit only on V2L — never two earth references in parallel.
- The **protective conductor (CPC/earth) is continuous and never switched** — you switch line and neutral, not earth.
- Main and supplementary **bonding** keep the installation's metalwork at one potential (BS 7671 Chapter 54 — §542 earthing arrangements, §544 bonding conductors).
- Prove it **by test**: RCD operation in both grid and V2L modes; for a TT island, a low and stable electrode resistance (Ra).
- Outbuilding → **TT** with a local electrode; indoors → **isolation transformer** keeping the one PME/MET earth. Designed and proven by a competent person.

**Where this stops:** This explains the earthing principle that governs every V2L decision. It is not a wiring recipe — the earthing arrangement, the bonding and the testing are for a competent person to design and prove.

> **Education, not an instruction to carry out the work** — This explains the principle. Electrical installation work of this kind is notifiable and must be designed, installed and tested by a competent person to the current edition of BS 7671. The floating-V2L-on-PME approach is contested — it is only ever valid designed and proven by test, and the vehicle manufacturer does not sanction it.

## The one principle behind every V2L earthing decision

Every electrical source needs exactly **one** neutral-earth reference. On the public supply that reference is made for you: the star point of the substation transformer is earthed, and the network brings that reference to your home (on most modern UK supplies as a PME / TN-C-S arrangement). A car's V2L output is a *separately derived* source. On the Hyundai Ioniq 5 it is reported to be **floating** — there is no internal bond between its neutral and earth — so until you supply one, there is nothing for an earth fault to flow back to and nothing for an RCD to operate against.

> **Confidence: inference** — The Ioniq 5 V2L output is floating (no internal neutral-earth bond). (Reported in field accounts and consistent with the design, but behaviour varies by adapter. The safe default is to treat the output as floating until it is bench-verified, because an RCD has nothing to operate against until a single bond exists.)

**Figure: Floating vs bonded V2L output.** A floating V2L output has no neutral-earth reference, so an RCD cannot operate; making a single neutral-earth bond on the source side establishes the reference and restores protection.

_Two states side by side. On the left, the V2L source as delivered is floating: line (L) and neutral (N) have no neutral-earth (N–E) reference, so a residual current device has nothing to operate against — the output passes a socket tester but offers no shock protection. On the right, a single N–E bond is made on the source side (only when on V2L): this establishes the earth reference so the RCD can operate. Make exactly one bond, never two in parallel. Bonding the V2L neutral to earth feels wrong but is correct — it is the source's earth reference, like the substation transformer's earthed star point._

> **A floating output looks fine but is not protected** — A floating V2L output passes a plug-in socket tester — yet it offers **no RCD protection** until the single neutral-earth bond exists. That is the dangerous 'looks fine' case the principle exists to close.

## One bond — and only one

Supplying that reference means bonding the V2L neutral to earth. It **feels** wrong — you have spent a career keeping live conductors away from earth — but it is correct: it is the exact equivalent of the substation transformer's earthed star point, just for your separately derived source. The rule is one source, one bond. The bond is made on the **source side**, and it is in circuit **only when you are on V2L** (typically through an auxiliary contact on the V2L contactor), so that you never have two earth references fighting in parallel — one at the substation, one at the car — at the same time.

> **§551.4.3.2.1** (BS 7671, confidence: inference) — A source supplying in island mode or as a switched alternative needs an independent means of earthing — it must not rely solely on the distributor's earth, which can be disconnected during network maintenance. _Reference only; standard text not reproduced._

## The protective conductor is continuous — you never switch the earth

A changeover switches **line and neutral** between grid and V2L. It must **never** switch the protective conductor (the earth / CPC). Earth stays continuous from every exposed-conductive-part back to the main earthing terminal at all times, in both modes and during the transfer itself. What changes between modes is *where the single neutral-earth reference is made* — never whether an earth exists. Switching a protective conductor would leave metalwork unearthed for the instant it matters most.

> **Switch L and N — keep E continuous** — Two-pole changeover of line and neutral; the protective conductor is bonded through, continuous, and never broken by a switch contact. The neutral-earth bond is the only earth-side element that changes, and it is made only on V2L.

## Main and supplementary bonding

Bonding is what keeps everything that *can* be touched at the **same** potential, so there is no dangerous voltage difference to bridge. **Main protective bonding** ties incoming metallic services (water, gas, structural steel) to the main earthing terminal. **Supplementary bonding** ties exposed- and extraneous-conductive-parts together locally where required. On a PME supply this matters even more, because a broken PEN on the network can lift all 'earthed' metalwork together — bonding ensures it rises *together*, removing the touch-voltage difference rather than leaving one part live relative to another.

> **Chapter 54 (§542, §544)** (BS 7671, confidence: inference) — §542 sets the earthing arrangements (earthing conductor, main earthing terminal, electrodes); §544 sets the protective bonding conductors and their sizing. The V2L earthing decision is a Chapter 54 decision, made by the designer and proven by test. _Reference only; standard text not reproduced._

Bonding-conductor **sizing** is set by Chapter 54 and its tables, against the size of the supply conductors — cited here by reference only, not reproduced. It is part of what the competent person calculates and records.

## Where the board is decides the arrangement

The single-reference principle is the same everywhere; how you realise it depends on **where** the essential board sits. There are two clean routes, and the full decision tree (with the diagrams) lives on the island-mode and method pages.

### Separate outbuilding → make it TT

Drive a local earth electrode and take every circuit protective conductor to the outbuilding's earth bar — continuous, never switched. Do **not** export the dwelling's PME earth to the outbuilding (broken-PEN risk); only line and neutral run over. Make the single V2L neutral-earth bond through a contactor auxiliary contact, so it exists only on V2L, and protect with a Type A RCD. This only holds if no metal pipe, structure or cable armour bridges the two earth systems — a stray metallic path silently re-imports the PME earth you were trying to keep out.

> **Earth-electrode design (with BS 7671 §542.2.2 / §542.2.4, Table 41.5)** (BS 7430, confidence: inference) — Electrode type, depth, soil resistivity and rod spacing set the earth resistance. Keep Ra as low and stable as practicable — an electrode with a high electrode resistance tends to drift across the seasons, which is the difference between an island that disconnects safely and one that does not. _Reference only; standard text not reproduced._

### Inside the dwelling → isolation transformer, keep the one earth

You **cannot** TT a single indoor sub-board: it creates a simultaneous-reach hazard with the rest of the PME-earthed installation — you could touch the TT-referenced metalwork and the PME-referenced metalwork at once. Indoors you keep **one** earth. An isolation transformer in the V2L feed galvanically separates the floating output; the single neutral-earth bond is made on the transformer **secondary** (on V2L), and the protective conductor stays continuous to the main earthing terminal. No second electrode, no neutral diversion, no indoor TT island.

**Figure: V2L / PME changeover earthing circuit.** On a PME (TN-C-S) supply the V2L island gets its own earth reference — the CPC stays continuous, the neutral-earth bond is switched in only on V2L, and a local electrode provides the earth.

_The diagram shows two sources feeding an essential board through a changeover. From the grid, line (L) and neutral (N) arrive at the changeover; the circuit protective conductor (E/CPC) runs continuously to the board and earth bar and is never switched. From the V2L source, L and N arrive at the other side of the changeover. A neutral-earth (N–E) bond is made only when the board is on V2L, providing the floating output its single earth reference. A local earth electrode connects to the earth bar. The point: every source has exactly one neutral-earth reference, and the protective conductor is continuous in both switch states._

## Proof is by test, not by reasoning

None of the above is settled by being correct on paper — it is settled by test. The earthing and bonding are proven, in **both** grid and V2L modes, before the arrangement is relied on.

- **RCD operation** confirmed by test in both grid mode and V2L mode — a floating output gives no RCD protection until the single bond exists.
- **Continuity** of every protective conductor confirmed end to end; the CPC is never interrupted by a switch.
- **One bond, only on V2L** — confirm exactly one neutral-earth reference is live in V2L mode, and none of it is left in parallel with the grid reference.
- **TT island:** electrode resistance (Ra) measured low and stable enough for reliable disconnection within the required time.
- **No metallic bridge** between the two earth systems (pipework, structure, cable armour).
- **Bench-confirm** the actual V2L adapter's neutral-earth behaviour before relying on it as floating or bonded.

## Where this fits

This page is the principle. For the branching design — outbuilding TT versus indoor isolation transformer — see the island-mode earthing and isolation-transformer pages; for why a floating output is the starting condition, see the floating-versus-bonded page; and for the whole journey end to end, see the cornerstone.

> **Not confirmed (safety-critical):** Whether Amendment 4:2026 changed anything for §722 / V2X / PME / open-PEN is Not confirmed — the public IET/BSI change material checked here does not identify a §722 / V2X / PME / open-PEN change in A4:2026. The existing §722 / PME / open-PEN material appears to carry forward from earlier amendments, subject to licensed-text confirmation; no A4-specific V2X/PME change is asserted on this page.

### How this is made and proven compliant

**What governs it:** BS 7671 Chapter 54 (§542 earthing arrangements, §544 protective bonding conductors) and Chapter 41 (§411 automatic disconnection of supply); BS 7671 §551.4.3.2.1 (independent means of earthing for an island/switched-alternative source) and §722.411.4.1 (PME / open-PEN protective measures); BS 7430 (electrode selection and resistance) read with BS 7671 §542.2.2 / §542.2.4 and Table 41.5, for the TT-island route

**Who may do it:** Design, installation, inspection and testing by a competent person. Altering the earthing arrangement, adding a changeover or altering the consumer unit is normally notifiable under Part P (England; Wales, Scotland and Northern Ireland differ).

**How compliance is demonstrated:** Initial verification to BS 7671 Part 6 with an Electrical Installation Certificate; RCD operation proven by test in **both** grid and V2L modes; For a TT island: electrode resistance (Ra) measured low and stable enough for reliable disconnection; Continuity of every protective conductor confirmed; one — and only one — neutral-earth bond confirmed live only when on V2L; No metallic bridge (pipe, structure or cable armour) between two earth systems

## FAQ

### Why does a V2L output need its own earth reference at all?

Because it is a separately derived source. The grid's neutral-earth reference is made at the substation; a **floating** V2L output has none, so until one bond is supplied there is nothing for an earth fault to return to and **no RCD protection** — even though a plug-in socket tester will show 'all good'.

### Why is bonding the V2L neutral to earth correct when it feels wrong?

It is the source reference — the exact equivalent of the substation transformer's earthed star point, made for your own source. Make **one** bond, on the source side, in circuit **only on V2L**, so you never have two earth references in parallel.

### Can I ever switch the earth in the changeover?

No. The changeover switches **line and neutral** between grid and V2L; the protective conductor (earth/CPC) stays **continuous and is never switched**. The only earth-side element that changes between modes is *where the single neutral-earth bond is made* — never whether an earth exists.

### Why can't I just drive an earth spike for an indoor board?

Because a single indoor TT sub-board creates a **simultaneous-reach hazard** with the rest of the PME-earthed installation. Indoors you keep one earth and use an **isolation transformer**; the TT route is for a genuinely separate outbuilding, designed and proven by test.

### How is the earthing actually proven safe?

By test, not by reasoning. RCD operation is confirmed in **both** grid and V2L modes; for a TT island, the electrode resistance (Ra) is measured low and stable enough for reliable disconnection; and the competent person confirms exactly one neutral-earth bond, continuous CPCs and no metallic bridge between earth systems.

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_Author: Martin — qualified UK electrician (BEng Mech Eng; vehicle mechanic)._
_Last reviewed: 14 June 2026. Written against: BS 7671:2018 + A4:2026._
_Status: reviewed. General information, not project-specific design advice._
_[How we source this](/methodology) — evidence hierarchy, confidence flags and source policy._

## Sources

1. BS 7671:2018+A4:2026 — Requirements for Electrical Installations (IET/BSI) — https://electrical.theiet.org/bs-7671-18th-edition-wiring-regulations/about-bs-7671/ (cited by clause only; standard text not reproduced)
2. IET — Amendment 4 updates to the 18th Edition — https://electrical.theiet.org/amendment-4-updates-to-18th-edition
3. BS 7430:2026 — Protective earthing of electrical installations (Code of Practice, BSI) — https://knowledge.bsigroup.com/products/code-of-practice-for-protective-earthing-of-electrical-installations (cited by topic; 2026 clause numbers not confirmed; standard text not reproduced)
4. V2L Workshop technical reference (internal) — verified design facts and confidence flags