6mm vs 10mm Cable for an EV Charger

For a typical 7kW home charger (that is 32A on single-phase 230V), 6mm² supply cable is common on ordinary run lengths, while an installer often steps up to 10mm² on longer runs to keep voltage drop within the limits in BS 7671. There is no single right answer: the correct size depends on your run length, how the cable is installed, grouping with other cables, ambient temperature and the installer's design to the regs. Before you go any further, it helps to know whether you actually mean the fixed supply wiring or the charging lead you plug into the car, because people use "cable" for both.

Are you asking about the supply wiring or the charging lead?

This is the single most important thing to get straight, because "6mm or 10mm" only makes sense for one of them.

• Supply or install cable: the fixed wiring an electrician runs from your consumer unit (fuse box) to the wallbox. It is measured in mm² (cross-sectional area), and 6mm² or 10mm² is exactly this. You do not choose it yourself: a qualified installer sizes it to BS 7671.
• Charging cable or lead: the Type 2 lead between the car and the charge point. It is measured in length (metres) and current (amps), not mm². This is what we make.

We make EV charging cables (the lead), not the installation wiring. For the supply cable and the install itself, use a qualified EV installer. If you landed here because you want a lead, the real question is length, and our length guide and the charging cables by car will sort you out faster than any mm² chart.

When is 6mm² typically fine for a 7kW charger?

On a lot of straightforward domestic installs, 6mm² is the size installers reach for first. It is rated to carry the current a 7kW/32A charger draws, and on a short to moderate run the voltage drop usually stays comfortably within the BS 7671 limits.

In broad terms, 6mm² tends to suit a wallbox that sits reasonably close to the consumer unit, with a clean installation method and nothing unusual about grouping or temperature. It is also easier to work with: thinner, lighter and cheaper than 10mm², so where it does the job there is little reason to oversize.

None of that means 6mm² is automatically correct for your home. The installer still has to confirm it against the actual run and conditions on the day.

When do installers step up to 10mm²?

The usual trigger is distance. The longer the run from the fuse box to the charger, the more the voltage drops along the cable, and at some point a larger conductor is needed to keep that within the regulated limit. A longer run often means going up a size, and 10mm² is the common next step.

Run length is not the only factor. An installer may also move up to 10mm² when:

1. The cable is grouped or bunched with other circuits, which reduces how much current it can safely carry.
2. It passes through a hot area such as insulation or a warm loft, where derating applies.
3. The installation method itself limits the rating, for example where the cable is clipped or enclosed in a way that holds in heat.
4. There is a case for a little future-proofing, so the circuit has headroom rather than sitting at its limit.

Again, this is the installer's design decision under BS 7671, not a rule you apply yourself. Two homes with the same charger can correctly end up with different cable sizes.

6mm² vs 10mm² at a glance

Treat every row as a tendency, not a promise. The only size that matters for your home is the one a qualified electrician signs off after looking at the actual circuit.

What else drives the cable choice besides size?

Cable type for the route

Size is only part of it. The route decides the type of cable too. Steel-wire armoured (SWA) cable is used for outdoor, buried or exposed runs because of its mechanical protection, while twin-and-earth is only suitable for protected runs indoors. Where a cable is buried, it has to be at an adequate depth with warning tape and mechanical protection as set out in the regs. Your installer handles all of this as part of the design, and you can see how it fits together in our guide to what an EV install involves.

7kW or something faster

The 6mm² versus 10mm² question is really a single-phase 7kW question. A 22kW charger is three-phase (roughly 32A per phase), and most UK homes are single-phase, so cannot run 22kW without a three-phase supply upgrade, which is uncommon, costly and involves the Distribution Network Operator. A three-phase install uses a multi-core armoured cable sized to the installer's design, not simple 6mm² or 10mm² twin-and-earth. If you are weighing speeds, see 7kW vs 22kW, do I need a 22kW cable and single-phase vs three-phase charging.

Your supply and load

If your main fuse and supply cannot comfortably take another 32A or so, the fix is not always a bigger cable. Installers often fit a CT-clamp load manager, so the charger eases off when the house is drawing heavily, rather than upgrading the whole supply.

Why you should not pick the size yourself

Installing or altering an EV charge point circuit in England and Wales is notifiable work under Part P. It must be done by a registered competent person, for example through NICEIC, NAPIT or Stroma, or notified to building control. Scotland and Northern Ireland have their own equivalents. DIY is only legal if it fully complies and is notified and inspected, and it is strongly discouraged for EV circuits.

The installer also notifies the DNO for an EV charge point, and some supplies or outputs need prior approval before the work can go ahead, which can add a little time. Choosing between 6mm² and 10mm² is one small part of a wider design that only a qualified electrician can complete safely. You can browse more background in our EV charging guides.

Where this leaves you

If you are planning an install, expect your electrician to assess the run and most likely use 6mm² on an ordinary length or 10mm² on a longer one, with the final call made to BS 7671 on the day. If you were really after the lead, that is a length question, so head to our charging cables by car and the length guide.

Frequently asked questions

Is 6mm or 10mm cable better for an EV charger?

Neither is better in the abstract. For a 7kW/32A charger, 6mm² is common on ordinary run lengths and 10mm² is used on longer runs to keep voltage drop within limits. The right size depends on your run and is decided by the installer to BS 7671.

Can I use 6mm cable for a 7kW EV charger?

Often yes on a shorter or moderate run, but not always. Whether 6mm² is adequate depends on length, installation method, grouping and temperature. Only a qualified electrician can confirm it for your specific install.

When do you need 10mm cable instead of 6mm?

Usually on longer runs, where a larger conductor keeps voltage drop within the BS 7671 limit. Grouping, heat, the installation method and a little future-proofing can also push an installer up to 10mm².

Does cable size change how fast my car charges?

No. The charger output and the car's onboard limit set the speed. The supply cable just needs to carry that current safely. A bigger cable does not make a 7kW charger faster.

Is the 6mm vs 10mm question about the charging lead I plug in?

No. Those sizes refer to the fixed supply wiring in mm², run by an electrician. The charging lead is measured by length in metres and by current, and is a separate thing you buy for the car.

Do I choose the cable size or does the electrician?

The electrician does. EV charge point work is notifiable under Part P in England and Wales, and the cable size is part of a design to BS 7671 that a qualified installer must complete, not a figure you set yourself.