Splicing 10mm2 cable into a Y

[jpadie]

I've got some 10mm2 t+e that needs to route into an external twin socket and into an EV charger.  Both on an external wall 

 

The cable is enclosed in rigid pvc conduit at the moment.  I'm using deta tte junction boxes.  Very small and shallow! 

 

What's a good solution for creating a high current splice in a small weatherproof adaptable box please?  

[ProDave]

I would not do that.  The 10mm straight to the EV charger and only to there.  Feed the other 13A outside socket from a different source, even a spur from a nearby ring final, in 2.5mm

[jpadie]

4 minutes ago, ProDave said:

I would not do that.  The 10mm straight to the EV charger and only to there.  Feed the other 13A outside socket from a different source, even a spur from a nearby ring final, in 2.5mm

 

It's a 40amp circuit so there is headroom

 

Unfortunately the EV charger can't take 10mm2 cable.  The receiving terminals won't take more than 6mm2 cable and needs a bit more of a bend inside than would be credible with 10mm cable.   I'd rather avoid restringing new cable.  

 

I can maybe go straight through the outside wall to take a spur off the ring main. That would leave me with needing to go from 10mm to 6mm cable.  Which I can do via an isolation switch or wiska. 

[MikeSharp01]

Won't you need to split and re-fuse the 2.5mm line - switch fused spur in a weather proof box.  Otherwise you could draw 40A through the 2.5mm cable which could turn out to be a very bad idea.

[Mattg4321]

Pretty sure IET code of practice says that EVSE must be on a dedicated circuit. Thats the only way I’d fit one anyway. 
 

I’m surprised that it can’t take 10mm2. What manufacturer and model EVSE is it out of interest?

 

Why has a cable been installed that is incompatible with the equipment it’s intended for?

[jpadie]

Installed that way because I wanted to make sure the installation was somewhat future proofed.

 

The EVSE I chose long after the circuit was installed.  It's a hive mini pro 3 and uses wagos to connect to the incoming mains.

 

You're right that there is a dedicated circuit requirement for the EVSE in the 2022 regs. 

[MikeSharp01]

So all you need to do is reduce down to 6mm at the very end, making sure the cable is clipped direct - ref method C. While scrubbing the 2.5mm spur and going another way with that. Alternatively you could discuss the definition of "dedicated" and spur the 25mm at the very end of the cable at the EV charger. I am dedicated, and vice-versa I hope, to my wife but we also have two kids🤔 to whome we are both dedicated.

[jpadie]

Here's another wrinkle perhaps.  The intention of the outdoor sockets was to provide for a granny charger; and in case cars ever started to take a higher power single phase charge.  So the sockets would be an EV charger of sorts.   

 

I doubt that changes the interpretation either but I like the way you're thinking!  

 

The last metre of cable will be pvc conduit enclosed rather than clipped direct.  The conduit will be saddled on the exterior wall.  Not sure what the defrosting tables say about that.  

[Mattg4321]

I wouldn't be using a granny charger unless in an emergency. No PEN fault protection and doesn't comply with Section 722 of BS7671. 

 

Step the cable down to 6mm2 and do away with the socket or supply from a local circuit.

 

If not familiar with Section 722 seek assistance.

[Carrerahill]

On 07/02/2025 at 22:45, jpadie said:

I've got some 10mm2 t+e that needs to route into an external twin socket and into an EV charger.  Both on an external wall 

 

The cable is enclosed in rigid pvc conduit at the moment.  I'm using deta tte junction boxes.  Very small and shallow! 

 

What's a good solution for creating a high current splice in a small weatherproof adaptable box please?  

You could take the 10mm² into a junction box, use high quality connectors, then continue on 6mm² onto the EV charger.

 

If you need to feed a socket, you could, take another cable out the connection blocks and into the fused connection unit, do it within 3m, then you can use a smaller cable cross section here so you can get it into your FCU (under BS7671 434.2.1) and drop it into a fused connection unit, de-rate to 13A and feed your socket from that.

 

There are other ways too, including a small din-rail module and some MCB's locally, but it depends on your situation, space etc. 

 

What run is your 10mm² cable and what size MCB is protecting it? I'd be making sure it is a 40A for the 6mm² cable.