Adding a spur to an existing socket

[gash2024]

I have a single socket that i would like to take a spur off as our storage under the stairs is the other side of the studded wall and i would like to put the wireless printer under there, at the moment the socket is used for the TV e.t.c
Would this be ok? the house is a 1986 build

 

[PrenticeBoyofDerry]

Providing the socket you wish to take the supply from, is not already a spurred socket, it is allowed!

 

[ericmark]

Ring Main

• ericmark
• 1 Jun 2009
• 6

IET Wiring regulation update

The picture shows what is allowed. It is unlikely that you will satisfy all the requirements of the regulations which ask for RCD on all sockets, and a full inspection and test after the work is completed however with the load you intend it is also unlikely to cause a problem.

What seems to be a problem with many DIY guy is to work out if the origin socket is part of the ring or a radial specially as although against the rules radials are taken from radials so having two of each wire in the socket does not always mean it's part of a ring. I would say if unsure use a fused connection unit (FCU) anyway to limit total load which can be drawn.

With your own house there is unlikely to be a problem. If however the work will be inspected by landlord for example then likely it will not comply with such an old house as although one does not have to upgrade existing stuff, any new stuff has to comply.

 

[Electrifying]

What seems to be a problem with many DIY guy is to work out if the origin socket is part of the ring or a radial specially as although against the rules radials are taken from radials so having two of each wire in the socket does not always mean it's part of a ring. I would say if unsure use a fused connection unit (FCU) anyway to limit total load which can be drawn.

What does that mean??

 

[ericmark]

What seems to be a problem with many DIY guy is to work out if the origin socket is part of the ring or a radial specially as although against the rules radials are taken from radials so having two of each wire in the socket does not always mean it's part of a ring. I would say if unsure use a fused connection unit (FCU) anyway to limit total load which can be drawn.

What does that mean??

I am sure you have found many times how a spur has been taken from a spur or some one have split a 4mm radial and extended with 2.5mm thinking they were working on a ring.

I am therefore uneasy at telling someone that as long as there are two cables at the origin socket they can add a spur, as that's only true if the cable is 2.5mm and the system is A1 to start with.

I also realise most DIY guys don't have any meter and to even try to explain how to test it is a ring will fall on stony ground. Yes I know it's simple one just rings between each pair but where do we stop? If we are going to explain how to ring between pairs then should we also explain how to test loop impedance and go/no go limits for the RCD.

We know they will not have access to our test sets and are therefore unlikely to comply with the regulations. The question is "Would this be ok?" and we know likely it will not be to the regulations but also likely it will be safe enough so what should we answer?

Yes it's OK
or
It may be OK but unlikely?

I did use the word radial instead of spur I realise.

I had always considered that a cable less than 3m (434.2.1) protected to a limit over the current carrying capacity of the cable that relies on the fuse in the plug or terminating FCU was a spur.
And a cable protected to within it's current carrying capacity as a radial.
However if you read the IET correction it refers to a cable protected by a FCU as a spur so clearly the two words are interchangeable. Which of course means using their wording you can take a spur from a spur which I see as very confusing.

It says:-Spur. A branch from a ring or radial final circuit.
But there is no definition for a radial and from the diagram 2008 Corrigendum a radial final circuit starts at the distribution board, where it is connected to a overcurrent protective device.

Hang on, in a house what circuits don't start at the distribution board, where they are connected to a overcurrent protective device? Answer is simple non! So using that it means all circuits are radials! Hum that's not right. Now if we start to add words of our own like "start but not finish" or say "and is not a ring" we could make some sense of it but we can't do that the IET and BSI do the defining so as it stands spur and radial mean the same. I agree they shouldn't but they do.

 

[gash2024]

There was a spur on it before but the extra socket was outside of the small room so i removed it, as far as i am aware the lights are on a ring so i would expect the sockets to be the same.

 

[Electrifying]

There was a spur on it before but the extra socket was outside of the small room so i removed it, as far as i am aware the lights are on a ring so i would expect the sockets to be the same.

I think it's time you stopped fiddling with electrics.

As for Ericmark's conclusion that a 'spur' is a 'radial' and vice versa - so they must mean the same thing.....I don't think so.

A radial is a 'layout' of a circuit which starts at the CU and runs to 'wherever it ends', with as many 'branches' as you like.

An 'RFC' is a 'layout' of a circuit that begins and ends at the same protective device, (normally in the CU).

A 'spur' is an 'addition' to a 'radial' or 'RFC'.

Three totally different things.

E.G.

1mm addition to a 1.5mm radial - a spur

1.5mm addition to a 1.5mm radial - extension of radial

1.5mm addition to a 2.5mm radial - a spur

1.5mm addition to a 2.5mm ring - a spur

2.5mm addition to a 2.5mm radial - extension of radial

2.5mm addition to a 2.5mm RFC - a spur

2.5mm addition to a 4.0mm radial - a spur

Simple, really

Which means that adding a '2.5mm radial' to a '2.5mm radial ciruit' is NOT 'against the rules', nor is it a 'spur' - you are just extending the circuit.

The only issue is deciding what the circuit actually is that you want to connect to - but if you can't do that, you shouldn't be fiddling with it anyway.


For the OP:

Assuming we're talking 2.5mm T&E

Confirm which protective device isolates the socket that you wish to connect to. (using safe isolation)

Note the rating of the protective device - if it's 15/16A or 20A then you should be ok to connect an additional socket to it.

If it's 30/32A, then the socket is either part of a 'ring final', or it's a 'spur' off a 'ring final'.
In this case, return to your socket, (whilst still isolated), and do 'end to end' continuity tests on all conductors.

If you get continuity, the socket is part of the 'ring' and you can spur off it.

If you don't get continuity, it's a 'spur' and you can't connect another 'spur' to it, unless it has it's own overcurrent protective device,(e.g. 13A FCU)
If you don't know how to do these tests - get an electrician!

 

[gash2024]

looks like a 15A to me but i shall have to check it tomorrow, there are two 30A, two 15A & two 5A, who ever wrote inside the cover made a few mistakes as a few things are crossed out and the writing is not very clear at all .
As for the previous spur it was not inside the wall, it had been added at some stage and the wire was very yellow so it had been there for some time, one note to make was that it only contained the 3 basic wires as do all the original sockets.
The items that will draw off the socket are a wireless printer and a light (with plug)

 

[gash2024]

Yes it looks like its radial, the fuse for the downstairs sockets is 30A and after popping a socket off thats under the CU i found just one cable running into it.
I am presuming that a RCD 30mA double socket would be ok to fit on the spur that i am going to take off and would provide enough safety?