Multiple FCUs

[securespark]

I forgot to ask ....

3 FCUs on one unfused spur contravenes the regulations....

What it 'contravenes' is the deemed-to-satisfy suggestions given in Appendix 15 of the regs - which, incidentally also do not mention having two FCUs on one spur (even though that's no different from a double socket). As often discussed, that doesn't mean that one cannot comply with the regs in ways not mentioned in that 'informative' Appendix.

so, the question .... What would you say if the 3 FCUs were supplied with a 4mm² spur from the ring?

Kind Regards, John.

YES IT IS!!!

Because 2 spurs is 2x 13A accessories and a double socket is 1x 13A accessory.

The days of two accessories allowed on an unfused spur went out with the 14th.

I shall stand with head held high as I get shot down...

 

[JohnW2]

What is your definition of 'an alteration' - since it clearly must be different from mine.

Subject to a disclaimer that I've not given this exhaustive thought, I'll say "anything which requires a certificate to be issued".

If an electrician connected a new shower or oven to an existing circuit, would (s)he issue a certificate? (genuine question, not rhetorical!).

Kind Regards, John.

 

[JohnW2]

...having two FCUs on one spur (even though that's no different from a double socket). .

YES IT IS!!! Because 2 spurs is 2x 13A accessories and a double socket is 1x 13A accessory.

Yes, very clever - that's techically correct, BUT ....

.... most of the concerns raised in this thread relate to the fact that a designer has to consider what alterations an unknown person may make in the future to hard-wired loads without giving adequate consideration to the suitability of the circuit for the new load. A fairly unlikley, but not impossible, scenario

With that in mind, we have the situation that a very high proportion of members of the general public have no idea that they should not plug two large loads into one double socket (indeed, I can't imagine how many instances there must be of a washing machine and dryer plugged into the same double socket). Do you therefore not think that it is at least as likely that Joe Public will do this as that our unknown person will change a hard-wired load into one that the circuit is not suitable for - and therefore that, no matter how technically correct your comment may be, a designer would be irresponsible to not take into account what Joe Public is quite likley to do?

Kind Regards, John

 

[EFLImpudence]

If an electrician connected a new shower or oven to an existing circuit, would (s)he issue a certificate? (

I do.

I would not be happy leaving with only a "The old one worked alright" statement from the homeowner.

Edit - A certificate should be given for every job.

 

[Paul_C]

Because 2 spurs is 2x 13A accessories and a double socket is 1x 13A accessory.

But everybody knows that a double socket could be called upon to deliver more than 13A. And it's pretty obvious that an FCU feeding a 1A load will only be called upon to deliver 1A, except under fault conditions. So from the practical viewpoint, it's rather ridiculous to say that you can feed a double socket which may have a connected load of over 20A but you can't use two FCU's with a combined load of 1 or 2A.

The days of two accessories allowed on an unfused spur went out with the 14th.

The 14th edition only permitted two sockets to be fed on a non-fused spur (or one twin socket). It limited stationary appliances to one only.

Although on a more general note for assumed demand on various circuits (not specifically rings), if you look at Table A.2 in the 14th edition you'll see that it specified that the assumed demand for a 13A socket must be taken as 13A, and the assumed demand for a stationary appliance to be the B.S. rated or normal current for that appliance.

 

[securespark]

...having two FCUs on one spur (even though that's no different from a double socket). .

YES IT IS!!! Because 2 spurs is 2x 13A accessories and a double socket is 1x 13A accessory.

Yes, very clever - that's techically correct, BUT ....

.... most of the concerns raised in this thread relate to the fact that a designer has to consider what alterations an unknown person may make in the future to hard-wired loads without giving adequate consideration to the suitability of the circuit for the new load. A fairly unlikley, but not impossible, scenario

With that in mind, we have the situation that a very high proportion of members of the general public have no idea that they should not plug two large loads into one double socket (indeed, I can't imagine how many instances there must be of a washing machine and dryer plugged into the same double socket). Do you therefore not think that it is at least as likely that Joe Public will do this as that our unknown person will change a hard-wired load into one that the circuit is not suitable for - and therefore that, no matter how technically correct your comment may be, a designer would be irresponsible to not take into account what Joe Public is quite likley to do?

Kind Regards, John

 

[JohnW2]

If an electrician connected a new shower or oven to an existing circuit, would (s)he issue a certificate? (

I do. I would not be happy leaving with only a "The old one worked alright" statement from the homeowner. Edit - A certificate should be given for every job.

That's what I thought - so, by BAS's definition, any change of a hard-wired load counts as an 'alteration', at least if undertaken by an electrician. A suggestion that the same work would not constitute an 'alteration' if undertaken by a non-electrician would be, to say the least, a little bizarre!

Kind Regards, John.

 

[JohnW2]

....

Yes, I did indeed write all that. Any comments?

Kind Regards, John.

 

[securespark]

Sorry John. I got all excited & quoted and posted all in one go without commenting.

Wasn't sure what you were getting at though.

 

[EFLImpudence]

That's what I thought - so, by BAS's definition, any change of a hard-wired load counts as an 'alteration', at least if undertaken by an electrician. A suggestion that the same work would not constitute an 'alteration' if undertaken by a non-electrician would be, to say the least, a little bizarre!

There are no definition options on a MEIWC, as on EIC (new, addition or alteration).
If the circuit had to be 'changed' then obviously this would be an alteration.


With regard to the shower change analogy mentioned above and ordinary people being more likely to change a fuse than an MCB.
This would be more like your proposal if the 7kW shower was protected by a 30A 3036. Having replaced with an 11kW the householder then replaced the 30A fuse wire with a higher rating 'because it kept blowing' without determining if the cable could handle the higher current.
The replacement being physically easy and the same as sometimes required from an unskilled person being the problem.

The discussion depends on whether we have to cover future incompetence.
Apart from there being so many scenarios, I do not think we do.
Any properly designed circuit can be wrongly altered whether complicated or simple.

 

[JohnW2]

Sorry John. I got all excited & quoted and posted all in one go without commenting.

Ah, no problem - there are few of us who haven't done that!

Sorry Wasn't sure what you were getting at though.

Fair enough- let me try to simplify/summarise/precis...

Most of the arguments in this thread have based on the suggestion that a designer should design on the basis of the hypothetical possibility than Mr A.N.Other might come along in the future and replace a hard-wired load with a much heavier load and change the associated fuse, without checking whether or not the cable is up to the increased load.

Someone then challenged my statement that two 13A FCUs were (in terms of potential load) no different than one double socket by pointing out that a double socket is not designed to carry 13A. However,as we all know, Joe Public generally does not know that. I was therefore suggesting that it's a bit ridiculous to imply that a designer should ignore something that thousands of Joe Publics are probably already doing (just by plugging things into sockets) every day but that he was obliged to design on the basis of incompetent things that Mr A.N.Other might possibly do (to hard-wired fixed loads) in the distant future.

Is that any clearer?

Kind Regards, John.

 

[JohnW2]

This would be more like your proposal if the 7kW shower was protected by a 30A 3036. Having replaced with an 11kW the householder then replaced the 30A fuse wire with a higher rating 'because it kept blowing' without determining if the cable could handle the higher current. The replacement being physically easy and the same as sometimes required from an unskilled person being the problem.

Indeed - and that's not just hypothetical - it happens. We even see cases where the householder has upgraded an MCB (but not wiring) in this situation.

This The discussion depends on whether we have to cover future incompetence. Apart from there being so many scenarios, I do not think we do. Any properly designed circuit can be wrongly altered whether complicated or simple.

As must be apparent, I totally agree. I do think we should design on the basis of things that the general public can 'innocently' do very easily (e.g. just by plugging things in or changing fuses) - e.g. I would not dream of having three 13A sockets (rather than 3A FCUs) run off a single unfused spur, even if they were labelled '3A max'. However, as I have been suggesting all along, the moment one is into doing things to hard-wired loads (or the fixed wiring of the installation), there is no limit to the stupidity/incompetence that could be perpetrated, so it is unrealistic and unreasonable to expect designers to try to 'design for it'.

Kind Regards, John

 

[securespark]

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.

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.

It hasn't happened to me or anyone else in my company, but I know someone it has happened to.

And it's not nice.

 

[ricicle]

Only this morning I installed 2 x 13A FCUs spurred off a ring final circuit. I am confident enough to know there is no technical problem with it.

 

[securespark]

What, 2 13A spurs on a single unfused spur off the RF?