Garage wiring options

[securespark]

Well, that is based on the often-debated question as to what the maximum 'rating' (load) of double sockets actually is.

The only load it is designed for under BS1363. We all know things have tolerances.
Cables have tolerances - we can happily draw far more than 26A off a piece of 2.5, for example, without detriment.

My folding camping chair says it will take no more than 100kg, but, believe me, I weigh a whole heap more than that! Yet I have used it for many years without any visible damage.

However, on the face of it (or rather, the rear!), a double socket is designed for a load no greater than 13A.

 

[PrenticeBoyofDerry]

Thanks, all, for the replies and the interesting debate

They can often be that way, as we each have differing ways of dealing with certain issues and interpret the guidance to the regulations differently.
Having inspected the socket in the kitchen I can confirm that its on a ring and that the existing garage socket is a spur is taken from this (on an RCD protected circuit.)

This raises an interesting question: Why whoever put the original spur in didn't just extend the ring into the garage?

Because they either did not know how to, they were lazy or because they knew a unfused spur off this circuit was acceptable.

As it stands there are three conductors in the terminals of the kitchen socket.

There conductors in each terminal? But that alone does not mean it is part of a ring final circuit, it could still be a radial circuit or dare I say a spur from a spur arrangement. This needs to be confirmed before you do anything more.

I hesitate to ask this as it could prompt another flurry of debate, but... Could I simply take one "side" of the ring through to the garage (assuming, of course, that there is enough cable to pull through) replace the 13A (spur) socket in the garage with a junction box, wire the new 13A socket from this then return the ring back into the kitchen socket?

You could, you could also extend within the joint being within the kitchen socket or extend not by a junction box but another by leaving the socket there and adding a second socket to a convenient location.

I could then wire the lighting spur from a fused, switched connection off of the junction box.

You could but I wouldn't.

 

[JohnW2]

Well, that is based on the often-debated question as to what the maximum 'rating' (load) of double sockets actually is.

The only load it is designed for under BS1363. We all know things have tolerances. ... However, on the face of it (or rather, the rear!), a double socket is designed for a load no greater than 13A.

I think you are probably seriously underestimating an uncertainty and debate which we have discussed at great length on many occasions. Manufacturer's information/specs is generally ambiguous, and I didn't really get anything particularly helpful out of the MK Technical Support folk when I spoke to them about this.

As I said, I think most electricians probably believe that the 'maximum rating' of a double socket is 20A (or thereabouts). As for BS1363, it specifies a 'temperature rise test' for double sockets at a total load of 20A (if I recall, rather surprisingly, 14A + 6A), not at 13A total, which seems consistent with that fairly widely-held view.

Of course, if the maximum load of a double socket is 20A, that is very convenient for BS7671 in terms of 'unfused spurs', since (probably coincidentally) 20A is also the minimum CCC allowed by BS7671 for the cable of a ring final.

Kind Regards, John

 

[EFLImpudence]

As I have said before -

Looking at it logically, both sides of a double socket can obviously handle 13A.
The socket construction is such that a piece of copper strip forms both sides of the L, N & E plug pin holders.
The current path to both sides is separate, i.e. not shared on this copper strip.

Therefore the only part which would have to carry 26A is the rivet which joins this strip to the conductor terminal.

It would seem such a small job to construct the socket so that it could handle 26A that it seems silly not to have made it like that in the first place.

In other words, when being introduced the designer must have purposely and definitely thought "Someone may plug in two 13A loads but I will only make it strong enough for 20A".

Why would they do that?

 

[JohnW2]

As I have said before - Looking at it logically, both sides of a double socket can obviously handle 13A. The socket construction is such that a piece of copper strip forms both sides of the L, N & E plug pin holders. The current path to both sides is separate, i.e. not shared on this copper strip. Therefore the only part which would have to carry 26A is the rivet which joins this strip to the conductor terminal.
It would seem such a small job to construct the socket so that it could handle 26A that it seems silly not to have made it like that in the first place. ... In other words, when being introduced the designer must have purposely and definitely thought "Someone may plug in two 13A loads but I will only make it strong enough for 20A". ... Why would they do that?

Quite so, it does seem bizarre - particularly given that, as I'm always saying, I'm quite sure that the vast majority of the general public (who, after all, are 'the users') have never even dreamed that a double socket could not safely supply 2 x 13A loads. ... so it almost seems like a 'designed-in hazard'!

However, it does seem to be at last partially true. There is the famous 'report' from MK, found on the IET forum (I don't think we've ever found 'the original'), which I have posted here more than once, indicating that significant damage occurs to their double sockets with sustained loads greater than about 22A total. Because they never define what they mean by 'socket outlet', some of the specifications (including MK's) can be taken (and is taken by some) to mean that a double socket can only supply 13A total. It's all very unsatisfactory.

It occurs to me that maybe we are looking at this the wrong way. As you say, if each half of the double socket can safely supply 13A 'indefinitely', it is very strange that they haven't made it able to provide 2 x 13A. It is perhaps that each half cannot safely provide 13A 'indefinitely'?

Kind Regards, John