I have fitted a spur to a double socket, however it was a tad tricky since the conductors were not long enough. Is it 'OK' to hide screw block connectors in the socket box ? The Muppet who originally fitted the surface mount dual socket over the original single socket recess did not manage to connect up the earth cable.. so I can't have made it any worse !
Simon
Yes that is fine.
Have you considered
as an alternative to a surface mounted double socket?
Adam
Sockets are normally accessible, so screw connector block can be used in this situation. But, it all depends on the current rating of the block you have used / are thinking of using to make all your connections in the recessed box.
A standard ring mains can carry up to 30 amps, split between two conductors sized at 2.5 mm each, so equaling 5 mm that should be connected to each outlet point.
If you are thinking of connecting both of the original ring supplies together and tapping from them to the original double and then the new single spur outlet. Then you will need connector block rated for at least
30 amps current loading to be sure it will cope safely with all situations.Don't think you can get away with the smaller 15 amp rated connectors because of the space restriction you have in the single back box. You could be asking for trouble if you do. You could, if you are worrying about the space, use two sets of 15 amp connectors, but do it safely by connecting one supply directly to the spur and from there to the double socket and from the double socket back to the second supply. Thus keeping the full ring supply to both outlets again.
Two sets of smaller connectors are easier to work with in the small space provided by a single sized back box. One set of connectors can be placed neatly at the back of the box, with the other set of connectors placed in a mirror fashion in front. So leaving more room for the conductors to be dressed safely within the rest of the space in the back box.
Good luck with the project, anywhoo.
Thanks for help, I think they must be 30A connectors but I will check this. Is it as well to run a second 2.5mm T&E to the spur connection box and use 4 terminal connectors then ? Is that what you are saying ?
Thanks for help, I think they must be 30A connectors but I will check this. Is it as well to run a second 2.5mm T&E to the spur connection box and use 4 terminal connectors then ? Is that what you are saying ?
No. What I mean is. You should have two cables supplying the double socket. These two cables connect from one socket to the other right round the house. So all the sockets are literally connect together to form what is called a ring mains supply.
Looking inside the existing single back box, you see the two cables ( grey cover) which both have a red and black covered conductor and a bare earth connecting center conductor.
Connecting them together in 30 amp rated block is fine, but then taking a 4 or 6 mm cable to the double socket, would be the proper way to do it. Then you can safely take a spur off to the new single outlet.
But an alternative is to connect the first supply cable (grey cover with red and black inside) in a lower rated 15 amp block and take new 2.5 mm cable to the new single spur outlet. From the new single spur outlet, take another piece of 2.5 mm cable back to the double socket. Also from the double socket, take another piece of 2.5 mm cable and connect it with a separate block to the second supply cable.
What you are doing is keeping the whole ring mains supply connecting with all the sockets again, but now including your new spur off. So your spur will not be a spur, but part of the actual ring mains supply.
If you don't understand any of this explanation, then do it your own way. But be aware of the limitations of the safe loading on your new spur.
OK! so to be /safe/ I will replace the bit of 2.5mm I put between the ring main and the socket with 6mm and it will be OK assuming they are
30 A connectors . Thanks for that.
If you have a crimping tool then just crimp some wire on the make them longer. Its easier than screw terminals but they are OK for what you are doing if you use ones that are big enough.
"Ring final circuit" is the proper name really. (ring mains are not used in domestic wiring)
Extending both existing sets of wires to allow them to reach the existing socket is the way to go. The spur can then be safely taken from the socket terminals.
15A connectors are not suitable. The current in any single cable in a ring circuit can exceed that.Generally its usually simpler to crimp a connection to one of the existing cables when joining new socket(s) into an existing ring in this way since the connectors are physically much smaller. Otherwise you can run out of box space with four cables to terminate.
There are no limitations of loading on a spur that you need to keep in mind really. If the spur is unfused then it can supply at most one single socket. That in itself limits the maximum load. (for more than one double socket you would require a fused spur - an hence a total load limit of 13A imposed by the fused connection unit).
=A0
This maybe needs clarification.
The rules SFAIUI are that a single spur - normally in 2.5mmsq cable, unless its route etc dictates a larger size - can feed only one fitting, but that fitting can contain either a single 13 A outlet or a pair (ie double) of outlets.
This is because a double 13A socket is counted as a single 13A fitting for assessing circuit loading (or at least was in the 16th IEE regs).
To feed more than one fitting on a spur, a fused connection unit must be wired into the spur. This may be placed anywhere along the spur before the first fitting. The fuse rating may be up to 20A, (but is often only 13A) as 20 A is the limit current for 2.5mmsq cable.
Two tentative suggestions which came to mind when I read the OP:
(a) dig out the old metal backing box & replace it with a 45mm deep one to give more room for a cable connector (which needs wrapping insulation tape or some other isolation from the other contents of the metal box & socket)
(b) replace the existing socket from which the spur is being taken by
2 separate sockets (both could be either single or double) in line with the ring cable to provide spare connection cable from the ring. Make sure the spur cable is aligned in one of the safe vertical/ horizontal zones of the new sockets & connect up, joining the 2 new sockets with a short extra length of 2.5mm sq cable.If it were my problem I would probably have used (b) as the end result doesn't look botched & it gives more socket outlets of which I find I never have enough.
HTH
Be interested to know just how a 15 amp connector block differs from the terminals found in a 13 amp socket?
The diameter of the hole is similar as are the fixing screws. If the cables being jointed are overlapped over the entire length of the connector so both screws grip both I'd say they'll make an excellent connection well up to handling any current the cable can.
Yup, sorry I was trying to word "a single double socket" IYSWIM, and got something that failed quite admirably ;-)
I was under the impression that is was usually counted as 20A rather than 13A...
Depends on the installation method somewhat - 20A is toward the lower end (i.e. de-rated by several factors).
They will be tested to different specs at the least. However the quality of socket terminations does vary greatly. Some do seem only just up to it.
(the TLC "ultimate" ones being my current favourite - nice large open square terminals that come with the screws already open, nicely colour coded for old and new wires, shallow depth fitting, decent earth terminations (x2) etc. And they are an attractive design as well)
The terminal current rating almost certainly assumes you are not overlapping the wires...
Indeed. But there's no reason not to when simply extending a wire.
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