B***er this - braincheck please, building regs

It's the bungalow again (*groan*)

IEE Wiring regs aside, which state that a CU should be "accessible", any reason not to put a CU on the first floor, in a fairly accessible place (down the end of an alcove off the side of a dormer, 4-6,5ft head height on a sideways slope, will be part of my "lab" (ie office)? This is not a newbuild, so as I understand from trying to read it, I can ignore Part M - correct or not?

Background...

Making final siting decisions for boiler, consumer unit and plumbing runs prior to subbing in a builder to mod some walls (I'm too scared to try matching exposed exterior brickwork).

Decided long ago to run services round the perimiter of the roof void. This is a good decision.

Later, got round to inspecting the void. Void would be too tight for plumbing, comms and power wiring plus the odd bit of 100mm ventilation ducting. Plus the hot pipes would make it hot to the detriment of the cables' current carrying capacity.

Then had an Archimedes moment (minus the running naked to the pub or whatever he did when he discovered getting in a brim full bath gets you a clip round the ear from mother for flooding the house):

Split perimiter into two sections, each with two adjoining external walls. Use one half for wet + air, the other for electrical. We can get to anywhere running along the upstairs floor joists from either end. Genius. Choice for wet side already determined by the bathroom, shower room and kitchen + water mains being generally near one corner of the house.

So that nadgered up my CU siting which was also on the corner. If I stick it upstairs, I can get it near the supply head (bonus), and the wiring drops right where I want it and it's well away from hot and steamy places.

All I know, if I were God, I wouldn't have done the Earth in 7 days. Day 324 would have been still deciding if fish should have legs ;-> Mrs God would of course be rolling her eyes.

Cheers (once again)

Tim

Reply to
Tim S
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I think that's okay.

Owain

Reply to
Owain

There's something in the IEEE that states the CU has to be within a distance from the supply meter, and if further then the cables from the meter to the CU have to be sized and protected.

Size the cables for the current they will be designed to carry, and then go one size up. For instance, if designed to carry 60A, then

10mm^2 is rated at 65A clipped direct, so you must use 16mm^2.

Also, with the CU "at a distance", a Residual Current Detector or Earth Leakage Detector Phase&Neutral isolation switch is required.

It's a variation of

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rule of thumb for "at a distance" is if I can touch both at the same time with outstretched arms - say about four feet or so. If your upstairs meter is near enough to the floor and the downstairs supply head is high enough up you could persuade youself that they aren't at a distance and use a normal P&N isolator and a couple of meters of 25mm^2. The reason for sizing for distant CUs is to avoid the expense of dozens of meters of expensive 25mm^2.

-- JGH

Reply to
jgharston

Hi,

Thanks for the detailed reply.

jgharston coughed up some electrons that declared:

I've been working to EDFs 3m rule, with 25mm2 tails (though I might stretch the point slightly to 3.5m - but I'll ask them, they have been known to agree to 4m where 3m was impractical). When the bloke comes to re-terminate the new tails to the meter, I might also happen to have a Wylex REC2 100A DP isolator (which is one of the exact models the RECs use) to hand and I'll see if he's prepared to mount that in his box - would be handy for any future messing about.

It's not a fused device, which is why it is good if I can stay within the 3m rule. Otherwise, it'll be another 80-90 quid for a big ugly switch-fuse on the wall somewhere.

This upstairs location is the closest practical place I can put it WRT the supply. I think I'll go with it. Simple is good (and cheaper!).

I really just wanted to see if anyone was going to say "Aaahhg - CU upstairs - can't do that!" for reasons that I can't readily imagine, but may have escaped me :)

Cheers

Tim

Reply to
Tim S

The usual cry is "arrgh! leccy meter upstairs - can't do that!" (from the leccy company), which means my tenants have to trek down two flights of stairs to read their meter.

-- JGH

Reply to
jgharston

No you can't _ignore_ Part M, it applies to virtually any alterations you carry out to any building (except dwellings), and you shouldn't make any building (including dwellings) any less compliant than before the work was carried out. However, a CU isn't regarded as a 'normal' control that just anybody would require day-to-day access to.

Reply to
Hugo Nebula

Why can't you put a small CCTV camera on the meter and modulate the signal into the in-house TV distribution system?

Your wiring appears to have the disadvantage of using an RCD to provide whole-flat protection, which is deprecated and I don't think would be compliant with Seventeenth Edition.

If the RCD is required to protect the submains then possibly a 100mA one on the submain and split 30mA ones in the flat CU?

Owain

Reply to
Owain

Hugo Nebula coughed up some electrons that declared:

Thanks Hugo.

This is a dwelling.

But...

A few bits of the house will be demonstrably improved, compared to now.

One case is better access to toilet in one of the two ground floor loo rooms. They may not exactly meet Part M (new builds) but not too far off and much better than the current set up. The wet room shower (with level access) is definitely an improvement.

Is this the correct spirit?

Cheers

Tim

Reply to
Tim S

For cables after your switch-fuse (a distribution circuit) the normal design rules of BS 7671 apply in respect of voltage drop, overload & fault current protection and earth fault loop impedance. There's no need for any arbitrary uprating of the cable size.

OTOH for meter tails protected by the DNO's cut-out fuse the sizing needs to be at least 16 mm^2 for a 60 A main fuse and at least 25 mm^2 for a 100 A fuse. (Larger sizes might be necessary if thermal insulation is present.)

Usually this would only be the case for a TT installation and a 100 or

300 mA time-delayed RCD should be used to provide discrimination. If buried in a wall at
Reply to
Andy Wade

Hugo Nebula coughed up some electrons that declared:

PS - thanks for clarifying that :)

Cheers

Tim

Reply to
Tim S

I don't have the regs to hand, but when I investigated some years ago, the cabling from the supply head to the consumer unit, if not

25mm^2 are required to be one size over the current capacity size. In addition, those cables (note to Owain, not the installation) have to be protected by RCD or ELCD. I should annotate my webpage with the relevant references.

When my library gets a copy of the 17th Ed I'll compare it with my

16th Ed to see where the differences are.

-- JGH

Reply to
jgharston

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