Planning position of Consumer Unit etc...

[JDLDIY]

Hi there, so the situation is that currently, the mains electric supply cable comes from the road to a meter, which is mounted in a recessed wall box on the front wall. From there, power is run to a consumer unit directly inside, behind the meter box, this is in our existing kitchen.

We are completely re-designing the house and our current kitchen won’t be in that location. Our new utility room will be in an extension located to the rear of our current house, about 10m from our existing front wall. So, am I stuck with the consumer unit in the current location, or can some really heavy duty cables be run the distance to a new consumer unit located in the extension? Ideally, I don’t want the CU where it is....

Many thanks for your advice

 

[EFLImpudence]

So, am I stuck with the consumer unit in the current location, or can some really heavy duty cables be run the distance to a new consumer unit located in the extension? Ideally, I don’t want the CU where it is....

It could, but that is only part of the problem.

There all all your circuit cables as well. They will all need extending.

 

[sparkwright]

So, what WILL this room eventually become?

 

[JDLDIY]

It could, but that is only part of the problem.

There all all your circuit cables as well. They will all need extending.

Thanks for your reply, yes, the whole house needs re-wiring anyway.

So, what WILL this room eventually become?

Many thanks, office/spare room, why do you ask?

 

[JohnW2]

Many thanks, office/spare room, why do you ask?

I presume that the question is his mind (which I would have asked about if he hadn't) is why the Consumer Unit cannot stay where it now is.

Kind Regards, John

 

[JDLDIY]

I presume that the question is his mind (which I would have asked about if he hadn't) is why the Consumer Unit cannot stay where it now is.

Kind Regards, John

Ah, I see, I thought he might be checking whether it was to be a bathroom...

It’s just not in a convenient place/room, so I wanted to see what my options are for moving it. But I won’t if there’s too much cost/complication/work involved in doing so.

 

[AndyPRK]

its better if the cable run between the meter and new CU position is under 3 meters.

 

[JohnW2]

It’s just not in a convenient place/room, so I wanted to see what my options are for moving it. But I won’t if there’s too much cost/complication/work involved in doing so.

I'm not quite sure what you mean by "not in a convenient place/room" in relation to a CU that you will presumably only need to have access to once in a blue moon, and particularly since it will "only" be an "office/spare room" (I could understand your not wanting a CU on the wall in your living room or dining room etc.). However, that's obviously your decision.

Just moving the CU would inevitably involve appreciable cost/work (and probably some 'disruption'), not the least because, as has been pointed out, all of the circuits (as well as the feed to the CU) would have to be extended.

However, you have said that "the whole house needs re-wiring anyway". If that's the case, and if you mean 'a complete re-wire' (if that is necessary), then at the time you have that done, I would not have thought that it would make a lot of difference (to cost, work or anything else) whether the CU is installed at the location of the present one or somewhere else.

Kind Regards, John

 

[EFLImpudence]

its better if the cable run between the meter and new CU position is under 3 meters.

It doesn't really matter - think flats?

 

[plugwash]

AIUI many DNOs have rules on the maximum length of cable between the meter and the customer's first protective device. Furthermore meters are designed for use with meter tails which, given the lack of RCD protection, are rather limiting in terms of acceptable installation methods.

The result is if you want the CU a long way from the meter you usually end up needing a switch-fuse located near the meter and then an armored cable from the meter to the CU location, perfectly doable but it does add cost and complexity.

 

[JohnW2]

AIUI many DNOs have rules on the maximum length of cable between the meter and the customer's first protective device.

They do seem to claim that, but I've never fully understood, bureaucratically/legally, let alone electrically.

Bureaucratically, they are not even responsible for, in ownership of or in control of the meter, let alone anything downstream of it. Electrically, I'm not sure what difference it is meant to make to (as they would request) add a switch-fuse close to the meter which could well have a similar sized fuse as the DNO's cutout fuse. In any event, in practice, if one gets the supplier (not DNO) to fit an isolator close to the meter, then neither DNO nor supplier has any direct control over (or knowledge of) what might subsequently be connected to that isolator.

As I see it, anything downstream of the meter should be compliant with BS7671, nothing more.

The result is if you want the CU a long way from the meter you usually end up needing a switch-fuse located near the meter and then an armored cable from the meter to the CU location, perfectly doable but it does add cost and complexity.

I agree that a switch-fuse is the traditional approach - although, as above, electrically speaking, it will (in TN installations) often/usually afford no more fault protection to the tails (of whatever length) than does the cutout fuse. In a TT installation, if one wants the tails (of any length) to have fault protection then one needs an RCD close to their origin, anyway.

As for SWA, that (or earthed conduit etc.) might be required if the tails were 'buried', just as it would for any cable, but I'm not sure that I see any reason for it 'just because they are 'tails'. Am I missing something?

Anyway, as far as the OP is concerned, I would think that, even if one went down the switch-fuse route, in the context of a CU move (or 'complete re-wire) that would represent a pretty trivial amount of "additional cost and complexity".

Kind Regards, John

 

[EFLImpudence]

They do seem to claim that, but I've never fully understood, bureaucratically/legally, let alone electrically.

I think it is due to a misreading of 434 - like Eric does when saying that ring circuit 2.5mm² spurs are limited to 3m.

 

[JDLDIY]

It doesn't really matter - think flats?

Many thanks

AIUI many DNOs have rules on the maximum length of cable between the meter and the customer's first protective device. Furthermore meters are designed for use with meter tails which, given the lack of RCD protection, are rather limiting in terms of acceptable installation methods.

The result is if you want the CU a long way from the meter you usually end up needing a switch-fuse located near the meter and then an armored cable from the meter to the CU location, perfectly doable but it does add cost and complexity.

Ok, so it is perfectly doable, excellent news. What's an AIUI and what's a DNO?

I think the pragmatic way forward may be to move the CU to the hallway, which could be within 3m, just left along the front wall and the other side of an internal wall. How are the tails routed in this case? The walls are cavity, but narrow cavities.

Many thanks

 

[JohnW2]

Ok, so it is perfectly doable, excellent news.

Almost anything is 'do-able. however, as I've said, particularly in the context of a 're-wire', I don't think that moving the CU would add much addituional complexity/work/cost.

What's an AIUI and what's a DNO?

"AIUI" is not an 'it' - it's an abbreviation/acronym for "As I understand it".

"DNO" is "Distribution Network Operator" - the organisation which supplies electricity to your property, and their responsibility extends only up to their 'service head' (with their own fuses), commonly called a 'cutout'. This is different from the 'Supplier' (the company who you pay for electricity) whose responsibility starts (and also more-or-less finishes) with the meter.

I think the pragmatic way forward may be to move the CU to the hallway, which could be within 3m, just left along the front wall and the other side of an internal wall. How are the tails routed in this case? The walls are cavity, but narrow cavities.

Fair enough - and, as I've said, I don't think the "3m" is of any great consequence, anyway. The electrician will decide on the appropriate type and route of the cables (and any other 'measures' required). Cables are, in general, not meant to be installed in wall cavities these days.

Kind Regards, John

 

[JohnW2]

I think it is due to a misreading of 434 - like Eric does when saying that ring circuit 2.5mm² spurs are limited to 3m.

Whilst you are right about eric's (and others') misreading of that reg, I don't think it's the reason for the "3m rule" for meter tails that we so often hear about.

I may be wrong, but I get the impression that DNOs often do mention/invoke that "3m rule" for meter tails 'themselves', without any reference to BS7671 (which they generally seem to ignore, anyway!).

As I've said, it seems that DNOs who say this are 'satisfied' by installation of a switch-fuse near the origin of the tails which contains a fuse of the same rating as their cutout one - which does not seem to make much electrical sense - at least, not to me!

Kind Regards, John