Hi. I want to add an FCU (3A fuse) from a double 13A socket. However the socket is presumably a spur as it is supplied by a single 2.5mmsq cable; it is not on a ring. Is this acceptable/within regs? FWIW the new cable from the socket to the FCU would also be 2.5mmsq. Thanks.
No, not really. The double socket on its own is the limit for what you can run on an unfused spur.
The correct solution would be to add a fused spur before the double socket, to feed it and any further accessories. You can then add your FCU to the double socket with no risk. This would however limit the total current dray of both sockets and the FCU to a combined total of 13A.
Why not replace the double with a fused four/three socket converter and add in the FCU using 2.5 mm cable. No chance of overloading the cable as the converters all have a 13A fuse.
Thanks John. Major impact on decorations (wall chasingh needed). But I thought that would be the case. Cheers.
Interesting, but I'm not clear about this. Wouldn't this just be equivalent (in terms of the regs) to taking the FCU off a spurred 13A single socket? I presume this is disallowed in the regs in the same way as taking the FCU off a spurred double socket.
What has an ex premiere and the honours system got to do with it?
john
Does it need to be a double socket, or would a twin socket do (i.e. two singles - one for a fused spur, one for a single socket - that would not require much chasing)?
Which has the same effect as doing what I said,
Not quite.. same protection but in different places.
One leg protected by the fuse in the sockets the other in the FCU vs. one leg protected by the FCU and the other by the plug fuse.
Strictly speaking against the regs. The correct way would be to fit an FCU at the start of the spur - and then you can do anything afterwards. But with such a small load I'd just go ahead.
This seems to be a decent solution. I'll replace the double socket by a single and the FCU. Only a little bit of enlargemet of the existing back-box space is needed. The max load would be 16A - 13A from the socket plus 3A from the FCU. Even if it's not to the letter of the regs, it's safe in terms of load and the decorative disruption is even less than I originally planned! Cheers, Steve
OK to run an FCU off a spurred socket?
ooops! I miss read the title :)
That isn't any more regs-conforming than the FCU hanging off a spurred double socket, assuming you still mean both fed from the single spur.
FCU can be anwhere along the spur, providing there are no accessories or branches before it. It doesn't need to be at the start of the spur because it's only required for overload protection, and not fault protection.
No, I actually meant using a twin backbox to install a fused spur and a single socket in the place of the existing double - saving cutting extra wall there - the spur feeding the socket, and then adding the FCU elsewhere as a continuation from the socket. Hence the new FCU and the single socket would end up both being fed via a fused spur.
Having said that, the OP's mis-interpretation of what I wrote (although not very clearly I admit!) is unlikely to result in bad things happening. Even if the upstream fused spur were omitted, the maximum load would be limited to what is achievable through a pair of 13A fuses
- so in reality no worse that with a double socket.
(the non conforming aspect being that the assumed load on a double socket is usually taken as 20A allowing for diversity, which is below the minimum rating for a cable used on a ring circuit (21A) - The same allowance is not usually made for a pair of single sockets or a single socket and a FCU however.
John Rumm coughed up some electrons that declared:
I don't think any double socket actually allows 26A to be drawn continuously.[1]
One of the manufacturers (possibly MK, can't find the reference, but I think it was mentioned on the IET forums > year ago) actually conducted tests and found that much over around 20A total load, their double socket started to overheat. At 26A it was well on the way to being dead, brown and hot.
[1] Check the small print on the back - some say 13A.Cheers
Tim
IIRC, BS1363 allows a max of 13A total to be drawn, and requires this to be written on the socket (which as you say, it is, pretty well always on the back;-). It requires all sockets to be tested at a higher current though; I have 21A in mind, but that might be the testing requirement for single sockets -- I've forgotten now and I don't have a copy of BS1363 anymore.
The MK ones always look like they would actually handle 26A OK, but there are plenty of others which don't look like they would.
Indeed - badly worded. I meant before any wiring accessories.
I actually did know what you meant.
As getting back boxes out of the wall can be a PITA, another option is to leave the double socket where it is an fit a FCU next to the double socket. You then take the wires (crimped and extended) that feed the double socket to the FCU instead of the socket. The load side of the FCU then feeds the double socket and any FCUs downstream.
A temporary lash up until it is time to decorate and sink cables into the wall is to feed the new FCU from a 3A fused plug using the double socket.
Adam
But don't stop you doing it. A recipe for disaster. Its why the new regs don't allow twins on 2.5mm spur cables when a 30A mains fuse is used. You can if its a 20A fuse.
The three and four ways are safer, they have a fuse.
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