Electrical question – EV charger on 2.5mm T&E?

For the electrical people out there….   When my house was rewired 6 years back I asked the electrician to run cable to front for future EV charger. The time has now come to get a wall box charger installed. Sadly, on inspection I only have 2.5mm twin and earth, with a 40a breaker on the end! Would I be able to run a wall box EV charger (7kw?) off this cable, and would I need to replace the breaker?

the length of cable run is 6m max and it’s in a floor void, no conduit.

replacing the cable would be a major upheaval hence me trying to make the most of what I’ve got!

thanks

A 3 pin slow charger, probably, with a waterproof outdoor socket?

A dedicated 7kw ev charger? No. Is my guess.

Any 7kw ev charger will probably be wired directly from the meter box to a dedicated fuse box and then the charger.

I’m not an electrician!

NO – IIRC 7 kw is 28 amps – very very marginal on a 2.5 mm cable.  Can you use the existing cable to pull a thicker one thru?

https://quickbit.co.uk/blog/electrical-cable-guides/twin-and-earth-flat-cable-technical-specifications/

https://www.projectev.co.uk/wp-content/uploads/2023/06/User-Manual-2023-EVA-07S-SE-2.pdf

32A Circuit protection in that manual ^^  Looks like a fatter cable is needed 🙁

You’ll need an electrician to certify it anyway, so they might have a plan

The cable going from the consumer unit to our 7kW charge point is muckle, maybe 20mm diameter armoured stuff so based purely on this I’d say not. It’s probably a similar run of ~6m but along the side of the house not in a void.

It would be possible to use that cable on certain units as some have the ability for maximum load management through the CT clamp, so you would set the charger to use a max of 24A and swap your 40A mcb for a 25A to protect the cable. The downside to that is an increased charging time.
You’ll need an electrician so it might be an easy job to change the cable and you may also need a different type rcd too

Would it be that bad to replace the cable?  A sparky may be able to use it as a drawcord, plus with rods and rodding cameras you can hook and poke through voids.  You could make it the original sparkies problem!

No it’s not Ok, an EV charger is like a small shower except it will run for hours not minutes like a shower, plenty of opportunity to overheat. You want it on a seperate MCB and bigger cable than that. It’s not a difficult job but to be done properly needs testing and sign off. If you do get an electrician to do it is your breaker box plastic or metal? If plastic you may need to have that replaced as well as plastic ones are no longer compliant with the regs.

Looking at mine, I’d say the cable spec between MSB and the charger should be thumb thick….

My employer fitted my EV charger, and not wanting to take on any liability for the existing installation, they fit some blocks on the tails between the meter/isolator and main MCB, then spur off separate tails to a separate enclosure and MCB to supply to the charger.

Saves the cost of replacing the main plastic MCB, although if I was paying for the works I would probably have got the plastic unit upgraded to metal anyway.

I’ve got a 7kW EV charger wired to a new build that was prewired for an EV charger.. according to the very helpfully documented consumer unit, the EV circuit uses 6mm2 cable for both Live and CPC and has a 40A MCB

As has been mentioned before, an EV charger has to be commissioned by a qualified sparkie and they won’t connect it to anything that’s not within regs. I’d say make it their problem but if you are booking a charger install through an installer company or through Octopus for example, they are likely to just take the cable from the breaker box out through the nearest outside wall and run it externally to where the charger is being installed.  Fishing under a floor with preinstalled cabling is outside the standard install and might be hard to convince them to do.

My old 7kw charger is on 6mm armoured cable to dedicated 32a C type MCB in a modern metal consumer unit.  consumer unit was upgraded in 2017, DNO upgraded the cut out to 80a in 2019, EV charger installed 2019. I give the wired connections a visual check every 6 months as the charger unit I have has a previous  history of plastics going brittle where the 6mm cable is wired into the charger, I’m pretty certain mine isn’t that generation, but I still give it a routine check for peace of mind.

You’ll need a 6mm on either 32Amp or 40Amp MCB.

2.5mm on a 40A is horrendous, I’d complain as that in no way complies – the cable rating for 2.5mm is around 21Amps.

A 2.5mm radial circuit should only be on a 20A breaker. If you want a 32A it’d need to be 4mm. I’d be putting that charger on a 6mm with a 40A breaker (as others have stated). The purpose of the breaker is to protect the cable from overcurrent.

No electrician worth their salt would have put a 2.5mm cable on a 40A. You’re quite within your rights to call him back and ask him where in the regs it states that that is acceptable.

IAAE

If plastic you may need to have that replaced as well as plastic ones are no longer compliant with the regs.

Are you a spark. Where does it say they just retrofit to current regs.

Installation of a new circuit would require it to be terminated to switch gear compliant with current regs .  A new metal consumer unit could be used as the sole distribution supply for the EV charger with close attention to the earthing arrangements required.  If you connect to a consumer unit containing incorrect rcds and or  plastic body then as above it is correct you would have to replace the complete consumer unit which in turn would mean a full test on all circuits controlled by said board. ? As the cable is way under size then a new install is required

A very non-stealth advert: Buy one of our Fastamps EV chargers. If you add another electric car in future, 2 chargers can be linked on the same circuit, so you won’t have to fit another cable!

We’re just about to release a WIFI version aswell, if you’re so inclined…