Multiple FCUs

[ban-all-sheds]

But you can enforce a design current of 9A maximum by connecting loads which cannot draw more than 9A in total, in the same way as you can enforce a 40A maximum current on a shower circuit by installing a shower which draws no more than 40A.

If you change a 40A shower load for one which is too large the cable will not be damaged. No danger will arise.

If you change the 9A load for one which is too high the cable could be damaged. Danger will arise.

Not at all. I think it would be justified for somebody working within requirements of BS7671 to issue a certificate. But that isn't everybody.

So what equivalent standard approved by a member of the EEA would you suggest people work to?

If you remove one part of a fixed installation and replace with another, then I'd say that's an alteration.

But you think that people can discharge their legal obligations regarding the safety of that alteration without following any formal methodology - basically just say "I'm sure that'll be OK", and it will be?

Does replacing a shower require a BS 7671 certificate?

As above for the oven.

So on the one hand it's an alteration to an electrical installation, but on the other it requires no testing, and does not need to be done to any recognised standards?

 

[ban-all-sheds]

Exactly. I can understand the viewpoint and concerns of those who are not happy with my '3A FCUs' with their hard-wired (small) loads, but what I totally fail to understand is why they apparently don't have exactly the same concern about the shower circuits.

Because by altering the shower load you cannot create a potentially dangerous overload.

By altering yours you can.



YOU changed YOUR design and asked me to comment, so DO NOT then react like that when YOUR NEW design elicits NEW responses from me.

 

[ban-all-sheds]

I haven't commented on the labels, but even without them, I would say that you have exercised reasonable skill and care in preventing the load on the spur cable from becoming 39A by connecting only loads which total 3A, 6A, 9A, or whatever the figure happens to be.

That doesn't surprise me, given that you either cannot, or obtusely will not, grasp what "reasonable" means.

No, but then neither John nor I have argued that to be the case, at least I'm not trying to say that. I'm not looking at it from the point of view of whether it actually complies with the requirements of BS7671 or not,

It seems to me that that's exactly what John was asking:

I was wondering whether anyone could think of any way in which a pedantic Jobsworth of a PIRer (or should that be EICRer) could have a problem with it?

What percentage would ask what those units are feeding, or what the person intends to use them to feed?

I don't think many, if any would.

But as you raise the possibility, I'll repeat the question with that addition.

Imagine reading a post here, or indeed on any electrical advice forum, like this:

"I've just moved into a new house, and I've found a spur from a ring main with 3 fused switches on it. They're all supplied by the same cable, it's not a case of 2 of them running from the 3rd.

Is this OK?"

What percentage of replies do you think would advise either putting them on the ring or rewiring it so that 2 are on the load side of the 3rd, or adding a 4th with all of them on the load side of that, what percentage do you think would ask what they were to be used for, and what percentage do you think would advise putting labels on the FCUs to prevent an overload?

But it's easy for any casual user to plug anything which can draw up to 13A into a BS1363 socket. It's not so easy to change two or three small hard-wired loads for heavier loads, since that requires changes to the fixed wiring.

Can you please tell me which regulations in BS 7671 have difficulty as a significant factor in defining requirements?

Mr. Homeowner has no need to complete it, because he doesn't have any particular need to be working within the confines of BS7671.

So what standards should he work within in order to ensure he meets his legally binding responsibilities?


Edited to remove misplaced unquoted text.

 

[JohnW2]

OK, gotcha. This is how I feel and obviously you feel differently, but I would still prefer to design and install as per the good book. You may feel otherwise, but I'm not confident enough to make changes to or ignore regulations while at the same time be absolutely certain those alterations are safe or that they satisfy building regs.

I think you have got that back to front (in terms of the post of mine you were responding to) and are instead referring to the issue mentioned when I started this thread. To attempt to clarify further the point I obviously have not been making clearly enough ....

If one accepts (as many people here, including you, do) that one has to design on the basis of what this infamous Mr A. N. Other may possibly do (incompetently) in the future, then I would think that you certainly should also design on the basis of what some Mr & Mrs Joe Publics are undoubtedly (and 'innocently') doing 'all the time' - i.e. plugging two heavy loads, potentially 2x13A, into a double socket. Do you agree?

If you do agree, that means that unless the (unfused) spur cable from the ring to a double socket is 'clipped direct' for the entirety of its path (which will often not be the case), use of 2.5mm² cable will not be compliant with the reg's requirements in terms of current carrying capacity - so do you often use 4mm² cable in those situations? (I rather doubt it!) ....

As I regularly tell my customers, if I make a mistake, I could find myself in court being questioned as to why I did (or did not do) a certain thing.

That's true of virtually all of us who work in a trade or profession, and a good few others as well. So how would you feel in that hypothetical court if you had installed a double socket on a 2.5mm² spur that was at least partially not 'clipped direct'? Do you feel you would be 'safe' by citing Appendix 15 of the regs, despite the fact that the Tables in Appendix 4 indicated a CCC of, say, 20A for your installation method and your knowledge that it was far from impossible that Mr/Mrs Public would plug 26A into that double socket?

Kind Regards, John.

 

[ban-all-sheds]

you raised the certification as if it were a criterion to define certain work.

Yes - it's spun out of my original suggestion, which I still haven't moved away from, that the requirement to issue a certificate could be what makes something an alteration to the installation.

 

[JohnW2]

Yes - it's spun out of my original suggestion, which I still haven't moved away from, that the requirement to issue a certificate could be what makes something an alteration to the installation.

.... but we are being told that virtually all work undertaken by an electrician results in a certificate, so do you still not feel inclined to move away from that definition of an 'alteration'?

Kind Regards,John

 

[ban-all-sheds]

it is unrealistic and unreasonable to expect designers to try to 'design for it'.

So you think it would be unrealistic and unreasonable in this case to put a 4th FCU in to supply the other 3.

Not much more to be said then.

 

[JohnW2]

So you think it would be unrealistic and unreasonable in this case to put a 4th FCU in to supply the other 3.

You must have a short memory, since I have said several times that, out of deference to views of some here, that is what I'll probably do. There's never been any suggestion that such a design is either unrealistic or unreasonable, the only discussion having been about how necessary it is.

The more general discussion (about how realistic and reasonable it is to design on the basis of the most incompetent imaginable possible actions of unknown people in the future) still stands.

Kind Regards, John.

 

[securespark]

I design and install to BS 7671: Amd 1. That allows me to install double sockets on an unfused spur. However, I prefer to wire accessories on the ring.

That still doesn't stop clients overloading a double socket. But I always tell clients that double sockets are still 13A rated and should not be overloaded and will put that in writing so that we both have a copy.

If I cannot put accessories on the ring, then I will install either triples for general appliances or fused spurs for stationary equipment, so as far as I can, I am limiting the potential abuse of accessories.

A lot of abuse is due to poor input at the design stage. For example, putting a double socket in a space designed for two washing appliances is asking for trouble.

 

[Paul_C]

If you change a 40A shower load for one which is too large the cable will not be damaged. No danger will arise.

If you change a 40A shower load for one which is too large and you increase the rating of the fuse or MCB supplying it, then the cable may well be damaged and danger will arise.

If you change the 9A load for one which is too high the cable could be damaged. Danger will arise.

Only if you change the 3 x 3A fuses for higher rated ones which then allow the cable to be damaged due to excess current. If you leave the fuses as they are and try to connect 3kW loads to the FCU, then a fuse will blow.

So how are the two scenarios any different in principle?

So what equivalent standard approved by a member of the EEA would you suggest people work to?

I wouldn't suggest any particular formal standard.

But you think that people can discharge their legal obligations regarding the safety of that alteration without following any formal methodology - basically just say "I'm sure that'll be OK", and it will be?

Where did I say that? I merely said that there is no obligation for Mr. Homeowner to issue a BS7671 certificate.

How {.....} dare you remark on that with a !

If you think for one second that I am arguing with you just for the sake of it you can {.....} .

And yet again you resort to insults and gutter language when anyone takes you to task on anything.

 

[JohnW2]

I design and install to BS 7671: Amd 1. That allows me to install double sockets on an unfused spur.

It does indeed - but do you believe that mention of use of 2.5mm² cable (without any mention of installation method) for such a spur in the ('Informative') Appendix 15 over-rides the more general requirements of BS7671 that design should aim to avoid cable current carrying capacity being exceeded?

That still doesn't stop clients overloading a double socket.

Precisely - which is why I would suggest that the only safe course is to regard the design current as being the maximum which householders could (and sometimes do) draw from such a socket. (yes, I know we can't stop them plugging ten fan haeters into a ring final, but there's an MCB in the circuit to protect it from that!)

But I always tell clients that double sockets are still 13A rated and should not be overloaded and will put that in writing so that we both have a copy.

As BAS has said (and I agree with him on this one) even sticking labels on sockets indicating current limitations would not turn non-compliance into compliance -so I'm sure that verbal instructions and bits of paper that the householder will probably lose do not have that effect, either.

Don't get me wrong - I'm not suggesting that I would ever even think of using 4mm² cable for such an unfused spur - but I'm trying to illustrate what happens if one gets too obsesed with compliance with the letter of the regs.

A lot of abuse is due to poor input at the design stage. For example, putting a double socket in a space designed for two washing appliances is asking for trouble.

Totally agreed, but it seems to be a very common practice. In fact, single sockets seem to be quite a novelty these days.

Kind Regards, John.

 

[Paul_C]

I haven't commented on the labels, but even without them, I would say that you have exercised reasonable skill and care in preventing the load on the spur cable from becoming 39A by connecting only loads which total 3A, 6A, 9A, or whatever the figure happens to be.

That doesn't surprise me, given that you either cannot, or obtusely will not, grasp what "reasonable" means.

Do you consider a twin socket outlet on a non-fused spur to be reasonably safe, even though it's entirely possible for somebody to plug in a 26A load?

It seems to me that that's exactly what John was asking:

I was wondering whether anyone could think of any way in which a pedantic Jobsworth of a PIRer (or should that be EICRer) could have a problem with it?

Maybe, but I was taking it more along the lines of a complaint that it was unsatisfactory or "needs improvement," rather than whether it doesn't comply with BS7671 but would be only a code 4.

What percentage of replies do you think would advise either putting them on the ring or rewiring it so that 2 are on the load side of the 3rd, or adding a 4th with all of them on the load side of that, what percentage do you think would ask what they were to be used for, and what percentage do you think would advise putting labels on the FCUs to prevent an overload?

Probably a substantial majority on the first option, because there's a tendency here to recommend whatever the current version of BS7671 says rather than to actually think it through logically. The labels - Well, personally I doubt it would be suggested at all.

But it's easy for any casual user to plug anything which can draw up to 13A into a BS1363 socket. It's not so easy to change two or three small hard-wired loads for heavier loads, since that requires changes to the fixed wiring.

Can you please tell me which regulations in BS 7671 have difficulty as a significant factor in defining requirements?

What does that have to do with it? I acknowledged several pages back that the arrangement does not comply with BS7671.

So what standards should he work within in order to ensure he meets his legally binding responsibilities?

Any or none in particular, so long as what he does has made reasonable provision for safety.

If one accepts (as many people here, including you, do) that one has to design on the basis of what this infamous Mr A. N. Other may possibly do (incompetently) in the future, then I would think that you certainly should also design on the basis of what some Mr & Mrs Joe Publics are undoubtedly (and 'innocently') doing 'all the time' - i.e. plugging two heavy loads, potentially 2x13A, into a double socket.

Precisely. If one is supposed to allow for Mr. Other coming along, disconnecting a fixed appliance from an FCU, connecting a much more powerful appliance to the same FCU, and upgrading the fuse in that FCU from 3A to 13A, then one should, surely, also allow for Mr. or Mrs. Publics simply plugging two 3kW heaters into a double socket, which requires considerably less effort?

As I regularly tell my customers, if I make a mistake, I could find myself in court being questioned as to why I did (or did not do) a certain thing.

As John has asked already, couldn't the same be said of a double socket on a non-fused spur?

"Mr. Spark, Did you not consider the possibility that Mr. & Mrs. Public might plug both a clothes dryer and a portable fan heater into the twin socket you fitted in their utility room?"

So you think it would be unrealistic and unreasonable in this case to put a 4th FCU in to supply the other 3.

Would it be unrealistic and unreasonable to provide protection for a non-fused spur cable feeding a twin BS1363 socket outlet?

But I always tell clients that double sockets are still 13A rated and should not be overloaded and will put that in writing so that we both have a copy.

So assuming for a moment that you were not tied to working to BS7671, would you be happy to do a similar thing for the three FCU's in John's scenario? That is put it in writing that those FCU's are suitable for appliances installed at the time, but that those appliances should not be changed for more powerful ones without expert assessment as to whether the existing circuit arrangement is suitable?

 

[securespark]

I design and install to BS 7671: Amd 1. That allows me to install double sockets on an unfused spur.

It does indeed - but do you believe that mention of use of 2.5mm² cable (without any mention of installation method) for such a spur in the ('Informative') Appendix 15 over-rides the more general requirements of BS7671 that design should aim to avoid cable current carrying capacity being exceeded?

I refer the honourable gentlemen to my previous response: I avoid using double sockets on an unfused spur.

That still doesn't stop clients overloading a double socket.

Precisely - which is why I would suggest that the only safe course is to regard the design current as being the maximum which householders could (and sometimes do) draw from such a socket. (yes, I know we can't stop them plugging ten fan haeters into a ring final, but there's an MCB in the circuit to protect it from that!)

That is what I do: I don't put double sockets on unfused spurs.
However, I also have to work with installations that others have done where double sockets are being abused.

But I always tell clients that double sockets are still 13A rated and should not be overloaded and will put that in writing so that we both have a copy.

As BAS has said (and I agree with him on this one) even sticking labels on sockets indicating current limitations would not turn non-compliance into compliance -so I'm sure that verbal instructions and bits of paper that the householder will probably lose do not have that effect, either.

Maybe not. But at least if I end up in that court, I can waggle those bits of paper at the geezer in the funny wig and hold my hand on my heart and say that I have done my utmost to try and educate the client so as avoid any danger arising. However, these bits of paper would refer to another's installation as I would not install something like that.

Don't get me wrong - I'm not suggesting that I would ever even think of using 4mm² cable for such an unfused spur - but I'm trying to illustrate what happens if one gets too obsesed with compliance with the letter of the regs.

You don't need to get obsessed:just take certain precautions when installing. Just because 7671 says you can do XYZ does not mean you have to, especially when there is a safer alternative.

Apologies for the quoting, which has all gone to cock. I can't be bothered changing it as I'm off to bed soon!

 

[securespark]

"Mr. Spark, Did you not consider the possibility that Mr. & Mrs. Public might plug both a clothes dryer and a portable fan heater into the twin socket you fitted in their utility room?"

But I would not install such a socket.

But I always tell clients that double sockets are still 13A rated and should not be overloaded and will put that in writing so that we both have a copy.

So assuming for a moment that you were not tied to working to BS7671, would you be happy to do a similar thing for the three FCU's in John's scenario? That is put it in writing that those FCU's are suitable for appliances installed at the time, but that those appliances should not be changed for more powerful ones without expert assessment as to whether the existing circuit arrangement is suitable?[/quote]

Tied to 7671 or not, I would, yes.

As I wrote earlier:

When I assess an installation for safety, I would not think, for example, that your RF circuit has three accessories spurred off each other, but they are only running low-current appliances so not a danger. I would record it as a potential at risk situation.

I can't quite see why I'm getting a bit of a grilling about documenting a potentially at risk situation.

At the end of the day, one of things I get paid to do is to flag up potential dangers that I spot in clients' homes. Indeed, if I failed in that duty, I would disciplined and most likely dismissed for gross misconduct.

I do that by using my 25 year's experience to compare what they have in their houses to the current version of 7671. As, I assume, do other professional sparks.

 

[EFLImpudence]

I would not think, for example, that your RF circuit has three accessories spurred off each other, but they are only running low-current appliances so not a danger.

Just out of interest -

If you came across the above, three FCUs side by side, how would you 'think' they were wired?
Having discovered that they are all 3A fuses, would you think that each subsequent FCU was wired from the load side of the previous FCU?

So that the second was protected by two fuses and the third by three?
Would you think the only logical way would actually be as is proposed?
Would you not have to check before any alterations?