Adding a single socket spur

[Mark Carver]

I've got a friend turning up later this month with his electric car.

He's going to want to charge it overnight, so he's bringing his 13 amp charging lead.

It's spurred me on (no pun intended) to fit a single outdoor socket on the front of the house.

Would seem easy. There's a 13A double socket inside on the same wall, so just drill a hole straight out of the back, and fit the outdoor socket 'back to back'.

However, I've had an explority examination. The inside wall is 'dab and dot' plasterboard. The metal backbox for the 13A internal socket is quite shallow, and screwed directly to the blockwork. I managed to pull one of the metal 'knockouts' out of the back of the box , so that has exposed a nice hole to drill through to the outside from.

Of course the socket is in a ring main,  I was going to add a bit of

2.5mmsq T+E straight out the wall, and into the back of an outdoor socket as a spur.

What worries me is given the backbox depth (25mm) and the existing pair of T+Es (they come in from above, through a grommet) is getting the third new T+E in place, and closing it all up again.

And the other worry, is presumably a 13A car charging leads pulls 13A continuously (?) so any 'imperfection' in screwing the terminals down on the indoor socket, and/or the wires moving as I shove the socket back into the wall, risks a hot spot. (Fortunately the indoor socket itself has nothing permanent plugged in to it)

[Andy Burns]

Probably only 10A for most granny chargers.

[Davidm]

Don't you want to be able to switch off (or isolate) that outside socket from within the house? I think I would. If so, simplest solution might be to drill a hole just below the existing socket and put a good quality 13 amp fused plug on the cable that feeds the outside socket. Then you can just unplug it or switch it off (if the indoor socket is a switched one).

[Andrew]

Apart from the need for a weatherproof outside socket, you might have to change the internal socket for one that accomodates three wires into each of the L and N terminals. Some makes seem to be better than others.

[williamwright]

I'd want any external socket to be on its own cable back to its own RCB. They get suicidal slugs etc in them and it's annoying otherwise.

[newshound]

The supply to my shed comes off a fused spur box with a switch and neon. Not actually ideal for a shed, but good for this sort of application. You have a switch so you can isolate it, and also a neon to warn you when it is on. You need a waterproof box outside (Screwfix had cheap doubles recently, also singles with an RCD iirc). But for occasional use can you just run the lead through a window? For cutting my front hedge, I just run the lead through a transom window to the hall sockets.

[Mark Carver]

I must admit, I adopted the 'stick a 13A plug on the end of a cable to feed it' solution Andrew suggested for my shed. It does the job. The biggest load in there is when I use my drill. Otherwise it's about 50 watts worth of LED lighting, and a WiFi AP

The irony is when I got the sparkie to rewire our place 18 months ago, I asked him to provide a 32A dedicated radial feed to the front of the house, ready for the day I have to fit a proper car charger. So the end of that cable is sat in a wallbox ready for that day !

[Scott]

Would there be any merit in fitting a 16 amp commando socket on its own circuit? I'm not sure whether the car lead is the same as a commando plug but it might be worth looking at options.

[Andy Burns]

So put a switched FCU on that to feed your "temporary" outdoor 13A socket?

[Mark Carver]

The only accessible points to that cable are inside the main CU, and outside by taking the lid off of the 'temporary'  outdoor wall box.

What would be a regs-compliant' method to fit a outdoor 13 A socket to that feed. (There's a 32A breaker in the CU)

[Scott]

Does he need one? I thought ring mains were fused at 32 amps anyway and sockets are connected to them. The fuse is in the plug, surely?

[Andy Burns]

JFDI, there's also a 32A breaker on your ring

[Andy Burns]

I think I'd like a switch to disable any outdoor socket.

Yesbut, they have two 2.5mm^2 cables running to them.

[Robin]

But another but is that a 32A radial will be 4mm or more (depending on length and derating)

[Tricky Dicky]

We have an outdoor socket, it feeds off the ring main through a switched FCU inside this means that not only is it protected with a 13A fuse but it can be switched off to prevent misuse not that it is easy to get to from the street.

Have you measured the depth of the back box you intend to spur off? Commonly for sockets either 25mm or 35mm are used both will allow a ring and a spur enough space for standard sockets, it will be a squeeze if you have low profile or flat plate type sockets but in those in cases the back box is usually the deeper of the two.

Richard

[Mark Carver]

It's a 6mm cable. Nothing is going to burst into flames, or 'go wrong' if I do stick a 13A socket on the end of it, so from that point view, as Andy says, JFDI. I wonder if the IEE Regs have any arcane reason not to approve doing such a thing ?

[Andy Burns]

MK sockets have terminals rated to accept

3 x 2.5mm^2, 3 x 4mm^2 or 2 x 6mm^ (stranded) so you should be ok physically, other manufacturers may vary.

If it was a dedicated car charging point, various earthing considerations would come into play, but since it's "just" an outdoor

13A socket, where someone might "incidentally" plug a car into it, the same as any other socket, can't see the problem.

[Mark Carver]

Yes, and as you've seen, I'm minded to move away from that idea now...

Yes, as stated 25mm depth to the back box. I could have added one of these to help, (as the socket is tucked away under a desk)

[Brian Gaff (Sofa]

How long might that take to charge a car, a lot of hours I'd suggest, also your bill for that day... ouch. Brian

[Brian Gaff (Sofa]

If its not used, just make it a spur and use it to switch the outside socket, you could even fit another socket inside somewhere where it might be of more use. Brian