FCU Feeding 2 Double Sockets - OK?

[greenstarthree01]

Hi all,

I had a similar thread a while ago but not wanting to necro-post it and also to try and ask a more specific question, I wanted to start a new one. So:

I have a double socket in a hallway, with 2 cables going into it, so assuming that it's either part of a ring circuit, or the mid-point of a radial.
I want to install a couple of double sockets about 5mts away under the stairs. The stuff in there will all be low power so 13A should be plenty. It's also only temporary until we have some building work done which will involve a re-wire downstairs anyway.

Original plan was to put in a fused connection unit and run a single 2.5mm T&E to the first under-stairs socket, then out of that and on to the second. This raised a couple of questions regarding layout:

• Does the original circuit being a ring or radial change the way this should be done?
• Can I keep the original socket where it is and go: ORIGINAL SOCKET > FCU > NEW SOCKET > NEW SOCKET
• If doing the above, could the FCU be put under the stairs with the new sockets, about 5m away, on the end of a single T&E cable?
• Or do I need to put the FCU in place of the original socket, eg: 2 ORIGINAL CABLES > FCU > ORIGINAL SOCKET > NEW SOCKET > NEW SOCKET?

Hope that's understandable, thanks all!

 

[flameport]

Does the original circuit being a ring or radial change the way this should be done?

Yes - if it's a radial, the FCU isn't needed.
If it's a ring, and that socket is on the ring, the FCU is required.
If it's already an unfused spur from the ring with 2+ sockets, it's already non-compliant and adding items to it isn't acceptable regardless of the methods used.

• Can I keep the original socket where it is and go: ORIGINAL SOCKET > FCU > NEW SOCKET > NEW SOCKET

• If doing the above, could the FCU be put under the stairs with the new sockets, about 5m away, on the end of a single T&E cable?

• Or do I need to put the FCU in place of the original socket, eg: 2 ORIGINAL CABLES > FCU > ORIGINAL SOCKET > NEW SOCKET > NEW SOCKET?

All of those are valid - but only if the existing circuit is actually a ring, and the socket is part of that ring.

You need to determine what the existing circuit is, the rating of the circuit breaker, size of the existing cable and whether it has an RCD or not.

 

[JohnW2]

Yes - if it's a radial, the FCU isn't needed.

Just to clarify for the OP ... if it's a 2.5mm² radial (protected by an appropriate {16A, 20A or 25A} fuse/MCB), then what flameport has said is correct.

However, if it were a 4mm² radial, protected by a 30/32A fuse/MCB, then the situation is essentially the same as with a ring - i..e. unless you used 4mm² cable for the spurred sockets, you would need an FCU.

If it is a ring, one option which often gets overlooked (seemingly because it is not one of the examples in 'guidance' in the regs) is, again, to run a spur in 4mm² cable (even though the ring is 2.5mm²). If you did that, you could run as many sockets off the spur as you liked, without an FCU.

Kind Regards, John

 

[greenstarthree01]

Wow, thanks for the info both. This forum pleasantly surprises me every time I use it.

the neatest option would be to put the FCU under the stairs with the new sockets.

2 CABLES > ORIGINAL SOCKET > SINGLE T&E To FCU > SINGLE T&E To NEW SOCKET 1 > SINGLE T&E To NEW SOCKET 2

If I understand rightly, this is ok as long as the original socket is part of a ring with no other spurs from it.
Flame port what I think you’re saying to check for is that the original socket isn’t already an unfused spur with another unfused spur taken from it?

I’m quite sure it’s not a radial given that all the sockets in the house are using 2.5mm T&E - if we had radial, wouldn’t I be seeing thicker cable used somewhere closer to the consumer unit?

Also, the other sockets downstairs mostly have 3 cables, with the sockets directly above them upstairs having 1, suggesting we have a ring downstairs with upstairs sockets spurred from them? The whole circuit is RCD protected but can’t remember the rating, not at home ATM.

This hallway socket is in a position where nothing is directly above upstairs so doesn’t have any spurs. At least that’s my reasoning!

Guessing there’s not a way for a DIYer to check for sure whether a socket with 2 cables is part of a ring or a non-compliant double spur?!

Thanks again

 

[JohnW2]

... the neatest option would be to put the FCU under the stairs with the new sockets.
2 CABLES > ORIGINAL SOCKET > SINGLE T&E To FCU > SINGLE T&E To NEW SOCKET 1 > SINGLE T&E To NEW SOCKET 2
If I understand rightly, this is ok as long as the original socket is part of a ring with no other spurs from it.

That's fine and correct.
Flame port what I think you’re saying to check for is that the original socket isn’t already an unfused spur with another unfused spur taken from it?

I’m quite sure it’s not a radial given that all the sockets in the house are using 2.5mm T&E - if we had radial, wouldn’t I be seeing thicker cable used somewhere closer to the consumer unit?

Not necessarily - one can have 2.5mm² radials. The clue will be in the rating of the MCB/breaker (or fuse) for the circuit in the CU. If it's 32A (or 30A) and the cable is 2.5mm², then (assuming it's been done right!), it should be a ring. If the breaker is 16A, 20A or 25A, then igt's probably a 2.5mm² radial.

Also, the other sockets downstairs mostly have 3 cables, with the sockets directly above them upstairs having 1, suggesting we have a ring downstairs with upstairs sockets spurred from them?

Very probable - but, again, at least in theory, not necessarily - you could have that same arrangement with a radial downstairs (in which case and sockets other than the last one would have 3 cables if something was spurred from it).

Guessing there’s not a way for a DIYer to check for sure whether a socket with 2 cables is part of a ring or a non-compliant double spur?!

Certainly no 'easy' way, unless you can actually trace the cables and see where they go.

Kind Regards, John

 

[greenstarthree01]

interesting. I can check the breaker when I get home shortly.
I could also trace the cables from that socket at least, but it would involve some under floor crawling!

I was wondering, regardless of ring / radial, if I went with connecting an FCU after the socket and then adding the 2 new ones after that... How is that different to plugging in a 5m extension lead and running it along the floor to under the stairs?
In terms of safety / protection I mean, they seem theoretically the same. Is it just the regs define what you can and can’t do with fixed cabling?

 

[greenstarthree01]

Well, to confirm, the breaker on this circuit is 32A. Wylex NHXB32.

I only have one 20A MCB on the whole CU and it’s feeding a totally different circuit with only two very close by sockets on it, presumed to be a very small radial in that case.

Every socket on the circuit has 2.5mm going to it, so it’s got to be a ring, unless it was done very very wrong?!

 

[JohnW2]

I was wondering, regardless of ring / radial, if I went with connecting an FCU after the socket and then adding the 2 new ones after that... How is that different to plugging in a 5m extension lead and running it along the floor to under the stairs?

Provided the socket was not already an unfused 2.5mm² spur from a 32A ring, it's not different (and perfectly acceptable) - in either case, you are 'limited' to 13A total by a 13A fuse (in an FCU or in the plug of the extensiion lead). Were yiou uynder the impression that this would not be allowed?

If it the socket was already an unfused spur such as I have described (and was a double socket), there would be a theoretical (but exceedingly unlikely!) risk that two 13A loads could be plugged into the existing socket and another 13A drawn by the new sockets via the FCU, making a total of 39A - which would be too much for the 2.5mm² cable feeding the spurred socket. In this case, if you plugged in an extension lead, it would be different - since that extension that would account for one of the 13A outlets of the double socket, so the max load in the cable feeding it would only be 26A.

In terms of safety / protection I mean, they seem theoretically the same. Is it just the regs define what you can and can’t do with fixed cabling?

See above.

Kind Regards, John

 

[plugwash]

Of course by stacking socket doublers you can connect as much load as you want to a 13A socket without pesky fuses getting in the way......

 

[JohnW2]

Of course by stacking socket doublers you can connect as much load as you want to a 13A socket without pesky fuses getting in the way......

What do you mean by 'socket doublers' - 'adapters' or single-to-double converters - or maybe something else? If you mean the former, although adapters are now almost extinct (because of lots of sockets and extension leads), those which exist would (should!) now have one of those pesky fuses in them!

Kind Regards, John

 

[plugwash]

What do you mean by 'socket doublers'

I mean an adapter, normally roughly cubic in shape with BS1363 pins and two BS1363 sockets.

https://www.amazon.co.uk/Masterplug...FAXBPNVW8CJH&refRID=7Y222YJZFAXBPNVW8CJH&th=1

If you mean the former, although adapters are now almost extinct (because of lots of sockets and extension leads), those which exist would (should!) now have one of those pesky fuses in them!

BS1363 does not require a fuse in a doubler. It does require fuses in adapters with 3 or more sockets and in adaptors to other socket types. Curiously the old doubler my mum bought while at university was fused, but all the doublers I have bought more recently have not been (though searching just now I find that CPC do sell a fused doubler).

To be fair you have to go out of your way to stack them because while the adapters themselves stack fine you can only get a plug into the top socket on every other adapter, but theoretically it gives you a way to connect unlimited loads to a 13A socket, using only plug-in consumer products without any pesky fuses getting in the way..

 

[JohnW2]

I mean an adapter, normally roughly cubic in shape with BS1363 pins and two BS1363 sockets.

That's what I thought - hence my comments about 'nearly extinct' and fuses!

BS1363 does not require a fuse in a doubler. It does require fuses in adapters with 3 or more sockets and in adaptors to other socket types. Curiously the old doubler my mum bought while at university was fused, but all the doublers I have bought more recently have not been (though searching just now I find that CPC do sell a fused doubler).

I didn't realise that - I thought that all such adapters (relatively rare though they are these days) now had (or should have) fuses, whether they had 2, 3 or however many outlets. Having said that, I probably haven't bought one for over 30 years, although I still have some knocking around, and probably some still in service!

I've just had a look in my cellar, and most of those gathering dust are 3-outlet ones (with fuses). However, there are a couple of ancient (certainly 30+ years) 'doublers' and, interestingly both have fuses.

To be fair you have to go out of your way to stack them because while the adapters themselves stack fine you can only get a plug into the top socket on every other adapter, but theoretically it gives you a way to connect unlimited loads to a 13A socket, using only plug-in consumer products without any pesky fuses getting in the way..

That (or the other students's trick of something 'solid' in place of the fuse in the plug of a 6-way extension lead!) would not have helped you very much in my daughter's student accommodation, since the couple of sockets in her room were on a 10A radial!

Kind Regards, John

 

[rsgaz]

I didn't realise that - I thought that all such adapters (relatively rare though they are these days) now had (or should have) fuses, whether they had 2,

Needs to be more than two; from BS1363-3 1995...

12.4

 

[sparkwright]

Only the very early two way adapters didn't have a fuse.

Certainly for the last 50 years or so all two and three way adapters have a fuse.

I fitted a cheap looking 3 gang converter socket in place of a double socket a few weeks ago. It is the first one I have seen that didn't have a fuse incorporated in it. Don't know what make it was, I didn't buy it. Can't be right can it?

 

[greenstarthree01]

Ah yes the days of plugging in two or three of those cubes and propping them up with something so they stay in the wall... I was a naive teenager who really needed that PlayStation running through the surround sound etc....