I am currently working on project' which is a new build youth club building of three stories and a basement. Customer wants the consumer unit of whole building to be installed on 2nd floor in the service cupboard inside a room. Can anyone suggest if it is compliant with the standards or not ?
Consumer unit
- Thread starter Harnoor
- Start date
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There's nothing in regulations that would prevent that.
The only point which might arise is if that means that the CU is fairly distant from the 'source' of the installation (essentially the meter), then it might be necessary to install a fuse at the upstream end of the connection to the CU - but your electrician will (hopefully!) know that.
Kind Regards, John
They used to want a fuse, and an isolator, close to the meter.
They seem to want a fuse if the feed to the CU is more than about 3m - and since such is almost invariably provided in the guise of a 'switch-fuse', then, yes, there is almost always an 'isolator' as well.
I'm not really sure that such a requirement makes much sense, since the fuse that people install when 'so required' is often of the same rating as the cutout fuse, hence essentially redundant!
Kind Regards, John
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Risk transference?
Their cut-out protects the length they allow (usually 3 metres).
So long as your own fuse is not more than that then the risk of what is downstream is up to you.
That way they do not have to make any further calculations. They have done their bit.
Their cut-out protects the length they allow (usually 3 metres).
So long as your own fuse is not more than that then the risk of what is downstream is up to you.
That way they do not have to make any further calculations. They have done their bit.
What is this magic of which you speak? Discriminating fuses?
How do the DNO ensure their fuse will not blow with faults past 3m given that the consumer's fuse will be no more than a couple of feet downstream of theirs.
Do you or they mean the consumer's extra fuse should be rated lower than the DNO even if the DNO fuse is 60A.
Ok.
So, allowing for the maximum Ze of 0.35Ω and 3m of 16mm² tails, that is a Zs of 0.357Ω so a PSSC of 644.506A.
Therefore with a CU 10m away that is an extra 7m of tails (still 16mm² for sake of exercise).
So, Zs is then 0.373Ω so a PSSC of 616.829A.
Therefore with a CU 20m away that is an extra 17m of tails (still 16mm² for sake of exercise).
So, Zs is then 0.373Ω so a PSSC of 581.175A.
All seemingly adequate for 60A or 80A fuse on 16mm² tails.
I know a line has to be drawn somewhere but given that this rule would apply to tails of 4m. it does seem illogical.
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I don't really get that, given that, as I said, the consumer-provided fuse will commonly be of identical (and presumably always 'similar') rating to the upstream cutout fuse.
To my mind, that means that the only potential advantage to the DNO is that if something happens which blows a fuse (or fuses), then there is a possibility (probably less than 50% probability) that theirs will not blow, so they won't have to attend to replace it.
However, I would think that, even if the 'tails' were very long, it is probably extremely rare that blowing of one (or both) of those fuses has anything to do with something happening to those 'tails' - so that the above argument would apply almost as much when the tails were 12 inches long as when they were 12 metres long - since they only 'require' the additional fuse for tails longer than about 3m.
I also wonder about this 'requiring'. I thought that DNOs had no interest in the meter, let alone anything downstream of it? Do they actually have any authority to dictate what happens downstream of the meter?
Kind Regards, John
They certainly used to have an interest, and could refuse to connect unless they were happy with the install.
Yes, that was certainly the case in the distant past. I can but presume that they then regarded themselves (or were regarded as) 'custodians of the safety of electrical installations' which went beyond considerations that could impact on their network
However, in recent times, their interest seems to stop at the cutout, even to the extent of there seemingly being differing opinions as to whether the 'tails' from cutout to meter are 'the responsibility of' the DNO or supplier.
Does anyone know of any current chapter and verse about any of this?
Kind Regards, John
I might have added ... if (these days) one reported to a DNO that the tails between meter and CU were in a dangerous state, I think it very probable that they would say that such an issue was "nothing to do with them", and say that the problem should be reported to the supplier. ... so why are they concerned about the protection of those tails, no matter how long they may be?
Kind Regards, John
EDF cover about 1/2 of my patch and they can be very difficult - to the point of not connecting if THEY are not happy
Yes, and it's not only EDF. DNOs seem to have invented their own set of rules and regulations, some of which make little sense to mere mortals.
I was thinking more on the lines of them accepting or expecting their fuse should blow for faults on their 3 metre portion and if it also blows on a fault past that on towards the far end of the universe they are not concerned as they have done their bit.
What happens to any protective device further down after the 3 metres they consider they are not responsible for.
If theirs blows or both blow they are not concerned really.
I will not disagree with that
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