Extending ring mains

[JoeJoe]

One of the sockets that I need is now hidden behind a chest of drawers, so I want to have a new one only about 1m away.

My plan is to disconnect one of the two cables going into the socket (it is definitely part of the upstairs ring, not a spur), extending it to reach the new socket, and run the return back to the original socket.

I intend to use crimps + heat shrinks to extend the cable, and run the new cable at the back of the wall, under the eaves - there is a small gap behind the wall that I can just about manage to squeeze through.

The wall both sockets are/will be fixed to is made up of plasterboard with 100mm celotex insulation behind it. I'd like to leave at least some of the celotex behind the backbox. Would it be enough to simply drill a hole through the celotex, just large enough for the two cables to go through, or does the hole need to be much bigger (the socket is likely to be used with a hair dryer)?

Is there anything wrong with my plan?

TIA

[JoeJoe]

PS: I want to extend the cable rather than run a new one as both cables connected to the inaccessible socket are fed from other sockets across the room, running under the floor, with carpet and chipboard flooring over (glued and screwed).

[Dave Plowman (News)]

Why not simply spur from the original?

[Roger Mills]

No - what you suggest will work ok. But wouldn't it be easier just to run a spur from the inaccessible socket rather than incorporating it into the ring? Your new cable can still run in the air-space behind the celotex without needing to take up any floorboards.

[JoeJoe]

Thanks guys.

I was thinking about a spur initially, but just wanted to do a "more proper/professional job"... ...and needed an excuse to buy a crimper ;-)

[ARW]

Because electricians and DIYers keep banging on about how much better it is to extend the ring?

Where in the real world a spur is fine for almost every application.

[JoeJoe]

First time I heard that from an electrician!

What about running the cable(s) through the celotex? Are there any rules?

Just wondering as it is likely to carry relatively high current. Would making the hole(s) slightly larger be enough?

[ARW]

It is not going to be carrying a relative high current. It will carry a short term 10A load when your wife dries her hair

It makes no difference if you extend the ring or use a spur. You should ensure sure that the current carrying capacity of the cable does not drop below 20A.

Appendix 6, table 6B of the OSG covers your proposed installation very nicely.

The CCC of 2.5mm T&E without any derating is 27A.

Passing the 2.5mm T&E through insulation gives a derating factor (determined by the length of insulation) as

100mm = 0.78 derating factor so your CCC is 21A.

[Adam Funk]

The thing I find curious is that (IIRC!) the limit on the number of unfused spurs is the number of non-spur sockets. So if you hit the limit & need another spur, you just add another socket to the ring & take the spur off that.

There's nothing to stop a future occupier from plugging two kettles in, though (I'm assuming it's a double socket). ;-)

[ARW]

In most cases it is all bollocks.

Apart from a kitchen what is the most likely demand on a ring circuit in

2015?

10A for a short while while the OH buggers around with her hair or 13A for a little longer when you are stripping wallpaper when redecorating?

The final ring circuit can easily cope with the hair drying and the wallpaper stripping at the same time.

It can even manage to boil two kettles from a double socket that are fed from an unfused spur in a bedroom if you wish to.

[JoeJoe]

Many thanks for taking the time - much appreciated.

[Dave Plowman (News)]

Modern kettles are generally 10 amps maximum.

[Fredxxx]

Most, yes. You don't have to look too hard for a 3kw kettle:

[Adam Funk]

Really? Ours isn't more than a couple of years old & it's the full

13 A.

What if you're trying to make a foundation?

[Dave Plowman (News)]

The vast majority use the standard kettle connector. Rated at 10 amps.

[spuorgelgoog]

10 British amps = 13 Chinese amps.

Owain

[Andy Burns]

Most kettles I've seen lately have the lead wired direct to the base plate with no IEC connector, just a "coax docking" connector ...

[Adam Funk]

I think you & I are thinking of the "cordless" kind (the jug lifts off the base, which is always live), whereas Dave is thinking about the other kind --- & I think he's right about the connectors on the other kind, although I'm a little surprised they (the kettles, that is) are limited to 10 A.

[Adam Funk]

Especially since kettles only run for a few minutes. I guess the only real potential problem is from high-power portable electric heaters (which aren't used so much now)?

[Dave Plowman (News)]

Yes - and they're generally 10 amps too.

I did look for a 'cordless' 3kW one some time ago with no success. Perhaps they are available now?

Perhaps it all due to making a universal product - many 230v countries have a 10 amp limit for sockets.