Can I change a spur to a single socket?

[Mottie]

The MIL has had French doors fitted that involved forming an opening in the rear wall and relocating a radiator to another wall. That radiator now prevents her using a twin socket as that is now behind the radiator and completely inaccessible (!). There is a switched spur with a neon on the rear wall that feeds just an outside socket. Would it be acceptable to change the fused spur for a single socket and leave the outside socket permanently wired in to the single socket or would that need disconnecting? It’s not a real problem to leave it disconnected as she only uses the outside socket to vacuum the leaves off of the artificial grass (!) and with French doors, she can now plug the vacuum into the single socket inside.

 

[Taylortwocities]

The fused & switched connection unit (FCU) may be a spur from a ring final.
You need to find out if the supply side of the FCU is a spur ( one cable) or part of a ring final (two cables). The way forward will depend on your findings.

 

[Mottie]

The fused & switched connection unit (FCU) may be a spur from a ring final.
You need to find out if the supply side of the FCU is a spur ( one cable) or part of a ring final (two cables). The way forward will depend on your findings.

So, if the supply is on a ring (two cables), I can leave the outside socket permanently connected (so it becomes a spur) but if the supply is already a spur (one cable), I must disconnect the outside socket because you can’t spur off of a spur. Is that right?

 

[JohnW2]

The fused & switched connection unit (FCU) may be a spur from a ring final. You need to find out if the supply side of the FCU is a spur ( one cable) or part of a ring final (two cables). The way forward will depend on your findings.

We know why you're saying that but, if it were me, I think I'd be inclined to preface your statement with something like "If you want to follow the ('informative') guidelines attached to the regulations, .....", so that the OP is 'fully informed'.

Even if the FCU is a spur from a ring final (which is quite likely), I am aware of nothing in the regulations themselves which prevents a single 2.5mm² (Method C) cable supplying two 13A outlets, whether that be one double socket or two single sockets - and, even more to the point, as we know, even those 'guidelines' explicitly allow it in the case of a double socket fed as an unfused spur from a ring final circuit.

Kind Regards, John

 

[conny]

There is also a possibility the FCU has been inserted into a radial circuit cable, (instead of using a JB, you will still have two cables to the load side), and then feeding the outside socket. In which case you can swap the FCU for another socket and still keep the outside socket.

 

[333rocky333]

As Conny says it could already be a Radial that was installed just for the External socket, worth looking to see what size mcb controls it, a Radial circuit will likely be 20amp, note the new socket will require Rcd protection

 

[conny]

A radial is also recognised in the CU as a single cable to the MCB, either 2.5 or 4mm If it's 4mm then no problem as you can have any, (reasonable), number of sockets on it.

 

[JohnW2]

I don't disagree with all this talk about it being possible that the FCU is on a radial - but 'common things are common', and I therefore think it's much more likely that there's a ring final and that this FCU is either 'on' that ring or (perhaps more likely) spurred from the ring.

Of course, unless there are things we haven't been told, there was no need for that FCU (be the circuit a ring or radial) if it's only supplying one socket. As we know, however, it's sensible to have a DP switch on the feed to an outside socket (in case the latter gets filled with water and trips an RCD, switching off lots of other circuits in the house!) - and maybe a FCU was used as a cheaper version of a DP switch!

As I have implied, if it were me I would probably not hesitate to do as the OP proposed (regardless of the nature of the circuit), since my personal view is that the actual regulations are more important than an (in my opinion, essentially rather silly!) bit of 'guidance' in an Appendix of the regulations!

However, as Rocky has pointed out, any new socket would have to be RCD protected.

Kind Regards, John

 

[plugwash]

I can certainly see where the authors of the guidance were coming from. A double socket is IMO less likely to see two large loads than two single sockets in distinct locations and on a 20A cable two large loads could easily be an overload.

Against that though, the current rating capacity of a 2.5mm T&E cable that is clipped direct or embedded in ordinary masonary is 27A, which is significantly higher than the 20A minimum required for ring cables and would be enough to supply two single sockets at full load. So in many (not all) situations the guidance is likely overly conservative.

P.S. The OP never said the outside socket was a single.

 

[JohnW2]

I can certainly see where the authors of the guidance were coming from. A double socket is IMO less likely to see two large loads than two single sockets in distinct locations and on a 20A cable two large loads could easily be an overload.

I don't doubt that such was probably their thinking, but they are just guessing/assuming, which is never a very good idea! Given what could be plugged into a double socket, if they believed that 26A would be too much, their 'guidance' should surely have been that only one single socket was 'acceptable', shouldn't it?

More to the point, they appear to be 'guiding' people to do something which, taken together with 433.1.204, might well cause people to do something which appears to be actually contrary to the regulations (433.1.1).

I can't tell you whether this was intended, but 433.1.204 can be easily read to be saying that the CCC of the cable forming an unfused spur from a ring final may be as low as 20A (e.g. 2.5mm² Method A, if one uses Table 4D5). If one has such a cable, and followed the guidance that it was OK for it to feed a double socket, then one would have a length of cable with a CCC of 20A which had 32A upstream over-current protection and 2 x 13A (i.e. 26A) downstream over-current protection - and I can't see why this would not violate 433.1.1.

In that case, guesses/assumptions are not required, because it's all about the ratings of the OPDs, not the guessed loading - i.e. although, given certain conditions, downstream over-current protection is acceptable to BS7671, 26A of downstream protection of a cable with a CCC of 20A is definitely not acceptable.

In terms of what is permissible for an unfused spur, one really has to rely on (comply with) 433.1.1 (and not the guidance of Appendix 15), since 433.1.204 itself says absolutely nothing specific (other than 'unfused spurs' are allowed from ring finals) - so could be read to be suggesting than an unlimited number of sockets could be supplied by an unfused spur.

P.S. The OP never said the outside socket was a single.

Yes, I noticed that. However, I felt that, should we discover it was a double, and given that we were told that it was only going to be used for very occasional vacuuming up of leaves, we could always suggest that it should be changed to a single!

Kind Regards, John

 

[Mottie]

Until I next go there, I can’t say whether it’s on a ring or a spur but the feed was used to power a single outside socket that was used for a vacuum cleaner. All she wants to power from the socket is a lamp.

 

[JohnW2]

Until I next go there, I can’t say whether it’s on a ring or a spur but the feed was used to power a single outside socket that was used for a vacuum cleaner. All she wants to power from the socket is a lamp.

So long as those are the only loads, the 'common sense' answer is obvious - and would remain obvious even if there were several sockets that one 'knew' were never going to be used simultaneous for large loads. However, some will undoubtedly argue that, at some point in the future, someone might plug 'ovens' or 'fan heaters' into both of them.

It therefore really comes down to regulations and, as I have tried to explain, even they appear to be happy with what you would like to do - it's only that (non-'compulsory') 'guidance' in an Appendix of the regulations which some people get excited about. I agree with plugwash that it's probably slightly more likely that two large loads will be plugged into two single sockets than into one double socket, but there can be no guarantee that that won't happen with a double socket - and even the 'guidance' says that one double socket is acceptable.

I think I've made it fairly clear wat I personally would probably do in your situation , but I think you've been given all the necessary information and obviously have to make the decision for yourself.

Kind Regards, John

 

[scousespark]

Mottie

The socket now behind the radiator is more of a concern. The regs have zones where it is permitted to run cables and these run horizontal or vertical from the socket. The risk is that somebody could drill into any buried cable, as the socket is hidden. There is also a requirement that all switches and sockets are accessible. You should move the socket or take it out of commision.

As for the FCU, you need to check if it is RCD protected and confirm it is in a ring. You can of course follow the diyer advice to carry on as you wanted to, as it will 'almost certainly' be a ring and it will be an FCU in the ring (as opposed to a spur from the ring).

 

[JohnW2]

You can of course follow the diyer advice to carry on as you wanted to, as it will 'almost certainly' be a ring and it will be an FCU in the ring (as opposed to a spur from the ring).

Good to see you. I hope all is well with you and yours.

If the above comment is a reference to me, what I actually wrote (in response to a comment that it might be a radial circuit) was ...

.... 'common things are common', and I therefore think it's much more likely that there's a ring final and that this FCU is either 'on' that ring or (perhaps more likely) spurred from the ring.

...so I'm not convinced that (if you were referring to me!) your comment necessarily qualifies a fair representation of what I had written.

Kind Regards, John

 

[scousespark]

Hi John. All well here and I hope all is well with you and yours.

I wasn't referring to you, rather that when a query is raised regarding FCU, the diy response tends to be that 'I changed an FCU for something else and it's fine.' I would just say it's always best to establish what is there, before changing. This is something electricians (most of us) do as a matter of course.