2 consumer units?

[JohnW2]

And you have suggested that the (or a) reason your interpretation is the right one, and the (or a) reason for having a single switch to isolate everything is the emergency scenario.

The two are so inextricably intertwined that I really don't think it is useful or helpful to try to distinguish between them. Although I, and others, have been talking about emergency situations, the actual need will often be for ('ongoing') isolation. For example, killing the electricity is not going to make an established fire go away, but isolation might well prevent secondary problems (and maybe further sources of fire) from arising.

Kind Regards, John

 

[ban-all-sheds]

I think you are being seriously over-sensitive. No-one has suggested that what you are saying is ridiculous.

On the contrary, that is precisely the suggestion being made.

Despite all you say about people being allowed to 'make their own decisions as to what is appropriately regarded as "an installation" in any particular case/context' when I say that it can be appropriate to designate a CU and its own circuits as an installation, and that the definition of "installation" in the regs fully support that, you then say

[paraphrase]Well if that is your decision about what an installation is then a microwave oven is an installation. If that is your decision about what an installation is then I must have hundreds of electrical installations in my house.[/paraphrase]​

Are you really claiming that you don't think it would be ridiculous to classify a single appliance as an electrical installation? Are you really claiming that you don't think it would be ridiculous to say that you must have hundreds of electrical installations in your house?

Are you really claiming that when you say "if you... then...", and the 'thens' are ridiculous that you are not suggesting that my if you is ridiculous?

When I said that it was perverse for someone to make a design decision with consequences they did not like when they could equally well have made a different decision without the unwelcome consequences, and JohnD said "I don't see that it is perverse, foolish, wicked or unsafe to have one main switch in a house, that turns off everything with one click of a switch", do you really think that he wasn't trying to make my position seem ridiculous? Firstly, I have not used the words "foolish", "wicked" or "unsafe", so why did he? Secondly, it is quite clear that what I said was perverse was not the possession of one main switch in a house, that turns off everything with one click of a switch (which would indeed be a ridiculous thing to say). What I said was perverse was unnecessarily making a decision which forced one to have such a switch whilst at the same time regarding the imposition of such a switch as a problem.

What is really crazy in all of this is that if someone has multiple CUs and wants a single switch to turn everything off then they can have one no matter how many installations they decide they have. Nobody needs to make the determination that multiple CUs are a single installation in order to be allowed to have such a switch.

Personal decisions being personal, they are very likely to vary - yet you seem to have been asserting that only your decision/interpretation can possibly be correct.

Please show me where.

 

[mwatsonxx]

BAS is correct, also a "single point of isolation" (even if provided) is difficult to achieve and can be illegal. Take buildings with generator and ups back up, or fed from different sections of the National Grid, only a person with an in depth knowledge of the installations could achieve total isolation, and it would not be a quick process. Also some buildings have "secondary supplies", and it is illegal for these circuits to be provided with a readily accessible means of isolation.

The golden rule with the interpretations of the regs is, your interpretation must be applicable to every type of installation in every type of buidling. If it can't, your interpretation is wrong.

Edit, corrected terminology

 

[JohnW2]

Are you really claiming that you don't think it would be ridiculous to classify a single appliance as an electrical installation? Are you really claiming that you don't think it would be ridiculous to say that you must have hundreds of electrical installations in your house?

No, I'm not. I agree that that both of those suggestions are ridiculous - but I am illustrating the fact that the BS7671 definition of an installation is so vague and wide ranging that, if one goes by "what the definition actually says" one could come to those ridiculous conclusions.

What I am not saying, and have not said, is that your interpretation of the definition is "ridiculous". It is just one of a spectrum of possible interpretations of a definition which could cover anything from 'all things electrical' in a large factory to a single appliance in a dwelling. Given what the extremes of that spectrum are, your interpretation is anything but ridiculous.

By the way, I have recently reminded the IET that it's been over a month since I asked them about interpretation of this definition. They have apologised for the delay and tell be that I will get a response 'soon'. Although any response I get will undoubtedly be covered in caveats, and will only be the opinion of one person (or, at least, small number of people, of discussions take place), it will be interesting to hear another view.

Kind Regards, John

 

[JohnW2]

BAS is correct, also a "single point of isolation" (even if provided) is difficult to achieve and can be illegal. ...

That may well be true, but it doesn't alter the fact that the regulations require a single point of isolation for each "installation" - so it again comes down to the question of how one interprets the definition of that word.

The golden rule with the interpretations of the regs is, your interpretation must be applicable to every type of installation in every type of buidling. If it can't, your interpretation is wrong.

That is largely true, but it's also true that a regulation has to meaningful to be worth having. If we have a situation in which the designer is free to decide how many 'installations' there are in, say, one large factory complex (the answer being anything from 'one' to 'dozens'), a regulatory requirement to have a single point of installation for each installation (as decided by the designer) is pretty meaningless.

... Take buildings with generator and ups back up, or fed from different sections of the National Grid ...

There is definitely a need for a clear definition, if the regulation is to mean anything. The interpretation I have been using, and which seems to me to be reasonable on the basis of common sense, is that (whether in a small house or a large factory complex) everything supplied by one 'incoming supply' (be that single- or 3-phase, LV or HV) constitutes "an installation". If a building has several DNO feeds, then I would say that each of those can reasonably be regarded as separate 'installations', but that everything fed from each of them constitutes a single 'installation'. That is the basis on which I believe that my house has just one 'electrical installation', even though it has a 3-phase supply with each phase being used separately.

Kind Regards, John

 

[ban-all-sheds]

Is it worth noting that when going from the 16th to the 17th they removed the "supplied from a common origin" from the definition?

 

[JohnW2]

Is it worth noting that when going from the 16th to the 17th they removed the "supplied from a common origin" from the definition?

Interesting. If there is not a 'common origin' then it would presumably be impossible to have a 'single point of isolation', at least electrically (but isolators relating to supplies from different 'origins' could be mechanically linked).

However, as I implied in my recent post, my personal inclination would be to say that things supplied from different 'origins' (which I take to mean different DNO supplies) probably should be considered as different installations.

Kind Regards, John