Is there any/much advantage to using 10mm2 cable for an EV charger instead of 6mm2?

StuB · 2026-02-20T11:41:33+0000

I've got an EV charger being installed by Octopus in a week or two and it's not the simplest of installs as the consumer unit is in the middle of the house however due to some other works occurring at the same time and with some effort and floorboard lifting on our part it looks like we should be able to sort it out between us.

The cable run from the consumer unit to the charger is about 15m and as standard I believe they'll install 6mm2 EV ultra cable which has a combined data cable.

About 12m of the cable would be indoors and the run from the consumer unit will be under floorboards and clipped directly to timber joists and walls. The areas under the floorboards aren't insulated.

Is there any/much advantage to me installing 10mm2 twin and earth and a separate data cable?

I'm primarily thinking about how warm the cable may get when it's in use with the cable under our floor attached to wooden joists.

Are there likely to be any increases in EV home charger power demands in the future?

6mm looks to be the normal choice and within spec and clearly Octopus won't be installing anything dangerous, just wondered if it's worth upspeccing it up while I have the chance.

Cost wise it's about the same as I happen to have a roll of 10mm2 twin and earth available however I will need to get some shielded ethernet as annoyingly I only have unshielded.

EFLImpudence · 2026-02-20T12:02:00+0000

StuB said:
Is there any/much advantage to me installing 10mm2 twin and earth and a separate data cable?

No.

StuB said:
I'm primarily thinking about how warm the cable may get when it's in use with the cable under our floor attached to wooden joists.

Why?
Clipped direct is the best installation method for current carrying capacity (maybe free air is 1A more).

StuB said:
Are there likely to be any increases in EV home charger power demands in the future?

Who knows what will happen? Maybe they will be banned.

StuB said:
6mm looks to be the normal choice and within spec and clearly Octopus won't be installing anything dangerous, just wondered if it's worth upspeccing it up while I have the chance.

No. It might never be needed.

StuB said:
Cost wise it's about the same as I happen to have a roll of 10mm2 twin and earth available however I will need to get some shielded ethernet as annoyingly I only have unshielded.

Don't bother then.

Why waste the world's copper?

StuB · 2026-02-20T12:11:36+0000

Thanks for an amazingly quick response and sanity check.

I just wanted to check I wasn't missing anything while I had the option to change.

JohnW2 · 2026-02-20T16:29:11+0000

StuB said:
Thanks for an amazingly quick response and sanity check.
I just wanted to check I wasn't missing anything while I had the option to change.

I agree with everything EFLI has written. In addition, you would have needed to consdier the question of whether Octopus would have been prepared to use your 'upgraded wiring' - something which I suspect is far from certain.

StuB · 2026-02-20T16:41:46+0000

JohnW2 said:
I agree with everything EFLI has written. In addition, you would have needed to consdier the question of whether Octopus would have been prepared to use your 'upgraded wiring' - something which I suspect is far from certain.

Thanks for the reply.

I've heard of a number of people having problems getting Octopus to install EV chargers when it's anything other than straightforward however in our case they've been quite good.

They have their rules and because it's not a straightforward install they sent someone out to do a survey which raised a few points that have now been resolved.

The same guy is booked to do the install and when he did the survey I asked him about using 10mm2 cable and separate data and he was happy with that as he can see the install route and thought it perfectly suitable and is happy with either option.

The person at Octopus I've been liaising with is also happy with either cable option.

They won't lift any floorboards but due to other works occurring at the same time this isn't too much of an issue for me to do for them.

Risteard · 2026-02-20T16:59:33+0000

I certainly wouldn't entertain using cable supplied by a customer. They are always told "no chance" when they ask, as I cannot possibly guarantee its quality or even whether it is a legitimate product, let alone specs e.g. reactance to fire. (Dca, -s2, d2, a2 being the minimum permissible grade for most of our works).

But you would never make the cost difference back with 10mm^2 for an EVSE, assuming that 6mm^2 is suitable in your case (it almost certainly will be) with reduced losses etc. And no, it will never exceed 32A/phase permitted, so future proofing it is nonsensical.

SUNRAY · 2026-02-20T17:08:23+0000

The only CURRENT benefit with using 10mm² would be not having to pay out for 6mm²

The only FUTURE benefit would be if it was being repurposed, say to feed a new garage containing the EV charger in a new location as well as other circuits.

If your fitter is happy to use your cable (I've heard many comments about Octopussy fitters having to adhere to their strict rules) then I'll say it's your choice.

StuB · 2026-02-20T18:19:55+0000

SUNRAY said:
The only CURRENT benefit with using 10mm² would be not having to pay out for 6mm²

The only FUTURE benefit would be if it was being repurposed, say to feed a new garage containing the EV charger in a new location as well as other circuits.

If your fitter is happy to use your cable (I've heard many comments about Octopussy fitters having to adhere to their strict rules) then I'll say it's your choice.

Thanks for the reply.

Cost isn't a huge driver in this decision, it's more about if there is some other reason to do it with the main ones being safety and heat.

10mm2 would actually work out cheaper as our install is between 10m and 20m so we had an additional charge from Octopus for £99.

As I have 10mm2 cable around there is no cost for that but I would need to get some ftp ethernet cable and as I don't need a whole reel it's fairly expensive and actually quite hard to find in short amounts so will probably cost me £40 or so making 10mm2 probably £60 cheaper overall.

That said I then become responsible for installing the cable and ensuring that it works so once that is taken into consideration it's effectively cheaper and less hassle to just let Octopus deal with it all.

Given the location of the charger I can't see the connection being used for anything else in the future as there is already power to the garage/workshop which is a distance from the charger.

Risteard · 2026-02-20T20:36:17+0000

StuB said:
Thanks for the reply.

Cost isn't a huge driver in this decision, it's more about if there is some other reason to do it with the main ones being safety and heat.

10mm2 would actually work out cheaper as our install is between 10m and 20m so we had an additional charge from Octopus for £99.

As I have 10mm2 cable around there is no cost for that but I would need to get some ftp ethernet cable and as I don't need a whole reel it's fairly expensive and actually quite hard to find in short amounts so will probably cost me £40 or so making 10mm2 probably £60 cheaper overall.

That said I then become responsible for installing the cable and ensuring that it works so once that is taken into consideration it's effectively cheaper and less hassle to just let Octopus deal with it all.

Given the location of the charger I can't see the connection being used for anything else in the future as there is already power to the garage/workshop which is a distance from the charger.

There is still a cost. It's not simply the extra cable length, but also the extra labour this involves which is charged. (Excuse the pun.)

And as pointed out, no reputable contractor will utilise cable which you have supplied.

SUNRAY · 2026-02-20T22:45:36+0000

StuB said:
Thanks for the reply.

As I have 10mm2 cable around there is no cost for that but I would need to get some ftp ethernet cable and as I don't need a whole reel it's fairly expensive and actually quite hard to find in short amounts so will probably cost me £40 or so making 10mm2 probably £60 cheaper overall.

It may be worth looking for a 20m screened patch lead

20m High Speed Cat 6 Ethernet Cable - FTP Shielded | eBay UK

And an earth wire to prevent electrostatic interference. [RJ45 Internet Cable 20m] Robust and flexible cable with reinforced RJ45 connectors on both ends. Plug and play, no tedious installation is required, just connect the high-speed Cat6 cable to your device, and you can enjoy a relaxed and...

www.ebay.co.uk

However: Cat6 https://www.ebay.co.uk/itm/405499289800?
Cat 5 https://www.ebay.co.uk/itm/226586379547?

StuB · 2026-02-21T01:20:08+0000

Risteard said:
I certainly wouldn't entertain using cable supplied by a customer. They are always told "no chance" when they ask, as I cannot possibly guarantee its quality or even whether it is a legitimate product, let alone specs e.g. reactance to fire. (Dca, -s2, d2, a2 being the minimum permissible grade for most of our works).

But you would never make the cost difference back with 10mm^2 for an EVSE, assuming that 6mm^2 is suitable in your case (it almost certainly will be) with reduced losses etc. And no, it will never exceed 32A/phase permitted, so future proofing it is nonsensical.

Risteard said:
There is still a cost. It's not simply the extra cable length, but also the extra labour this involves which is charged. (Excuse the pun.)

And as pointed out, no reputable contractor will utilise cable which you have supplied.

Thanks for your replies, I missed your one earlier.

I can understand not wanting to utilise cable or other items provided by a customer although in this case the installer was happy to do so. It probably helped that it's a nigh on full 100m reel of cable I have and it was available for him to see when he did the survey.

Anyway as cost isn't a big driver and it appears there are no real world benefits to using 10mm2 to save any potential hassle if there are any problems I've messaged them to tell them to supply the cable for the install along with everything else.

Hopefully it should all be sorted in a couple of weeks.

StuB · 2026-02-21T01:22:27+0000

SUNRAY said:
It may be worth looking for a 20m screened patch lead

20m High Speed Cat 6 Ethernet Cable - FTP Shielded | eBay UK

And an earth wire to prevent electrostatic interference. [RJ45 Internet Cable 20m] Robust and flexible cable with reinforced RJ45 connectors on both ends. Plug and play, no tedious installation is required, just connect the high-speed Cat6 cable to your device, and you can enjoy a relaxed and...

www.ebay.co.uk

However: Cat6 https://www.ebay.co.uk/itm/405499289800?
Cat 5 https://www.ebay.co.uk/itm/226586379547?

Thank you very much for that link, there are a few like that although I believe that is CCA cable so personally I'd avoid that for something like this. Solid copper is about double the cost.

As per my post above as there are no real benefits to using 10mm2 cable I've messaged Octopus to tell them to supply the cable when they do the install.

robinbanks · 2026-02-21T07:39:28+0000

StuB said:
I happen to have a roll of 10mm2 twin and earth available

Then use it, if you'll never use it for anything else. You use more of the world's copper buying additional cable

StuB said:
however I will need to get some shielded ethernet as annoyingly I only have unshielded.

Why? Chargers can work on 2G sim data speeds; they don't need gigabit and even if you can't get a couple of inches separation for the entire data run, and it introduces a tiny bit of interference and decreases the data speed slightly it will still be orders of magnitude in excess of what a charger needs to work

StuB said:
I believe that is CCA cable so personally I'd avoid that for something like this. Solid copper is about double the cost

you're installing a car charger that needs a data rate of about 100 bytes per second, and fussing about leads designed to carry data at rates of 1.25 billion bytes per second in supremely electromagnetically noisy environments. One AC cable tacked at the top of the joist, and an unshielded patch lead tacked at the bottom of the joist is so far the other end of the spectrum, it's not even worth considering. Even if your sparky is lazy and runs the two cables through the same hole in the wall, it won't make the slightest bit of differnce running parallel for such short a distance. Forum is panicking you over nothing here

StuB said:
the main ones being safety and heat.

You're massively overthinking this. If you already have the cable and they will discount the install for using it, use it. If you pay the same anyway, either use or sell your reel. If you're having big supply into your garage, buy your own sparky to use your cable to put it in, then tell octopus to connect wherever their rules say they have to

StuB · 2026-02-21T10:20:04+0000

robinbanks said:
Then use it, if you'll never use it for anything else. You use more of the world's copper buying additional cable

Why? Chargers can work on 2G sim data speeds; they don't need gigabit and even if you can't get a couple of inches separation for the entire data run, and it introduces a tiny bit of interference and decreases the data speed slightly it will still be orders of magnitude in excess of what a charger needs to work

you're installing a car charger that needs a data rate of about 100 bytes per second, and fussing about leads designed to carry data at rates of 1.25 billion bytes per second in supremely electromagnetically noisy environments. One AC cable tacked at the top of the joist, and an unshielded patch lead tacked at the bottom of the joist is so far the other end of the spectrum, it's not even worth considering. Even if your sparky is lazy and runs the two cables through the same hole in the wall, it won't make the slightest bit of differnce running parallel for such short a distance. Forum is panicking you over nothing here

You're massively overthinking this. If you already have the cable and they will discount the install for using it, use it. If you pay the same anyway, either use or sell your reel. If you're having big supply into your garage, buy your own sparky to use your cable to put it in, then tell octopus to connect wherever their rules say they have to

I'm completely with you regarding any network cable being fine for the data the charger would need but they use the data cable the CT clamp and I'm not up on how they work.

'Overthinking it' is pretty much the order of the day and as per my previous post I've messaged them to say carry on the install with their cable and as you say if I don't end up using the cable for the rest of the project then I'll put it on ebay.

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Is there any/much advantage to using 10mm2 cable for an EV charger instead of 6mm2?

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