Moving consumer unit....

Hi all,
I've just bought a house. it originally had a double garage and the CU was in the garage. One half of the double garage has been converted by a previous owner to a family room and the CU boxed in.
What I would like to do is move the CU to the unconverted part of the garage which means extending the meter to CU tails by a good 3m or so and extending the two ring mains, two lighting circuits, immersion and the cooker circuit to the new CU location.
I would be quite happy to replace the CU completely as the old one is of metal clad construction.
I would also like to separate out the kitchen & utility room sockets so that they are on their own ring main, run a separate MCB for new interlinked smoke/CO detectors, run a separate MCB for the new boiler, run a separate MCB for outside sockets run a separate MCB for outside lights run a separate MCB for loft sockets, a separate MCB for loft lighting. (this is because I plan to convert the loft at a later date)
I am capable of doing the job, but want to cover my backside legally speaking.
Has anyone here who is not Part P registered, moved a CU, added additional circuits and got it signed off OK by a Part P electrician or by Building control or was there too much hassle?
Or did you end up getting a sparky in to do the whole job?
The county of interest is Northamptonshire
Regards,
Stephen.
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Stephen H wrote:

Yes.
Our BCO is friendly and agreed to letting me produce an EIC provided I obtained some sort of qualification[1] (to cover his arse) and had a test instrument.
As I was rewiring the whole house, I would have had a test meter anyway - got a Megger 1552 off ebay and paid for fresh calibration cert.
[1] EAL Level 2 Domestic Electrical Installation (or something like that) - 2 weekends including exam. Course was actually useful as it covered testing in detail. In theory I should have the C&G for the regs too, but no-one's asked.
The EDF bloke who pulled the cutout fuse started off thinking I was a sparky and asked for my NICEIC number. I said it was a Part P job and had left my Megger conspicuously hanging on the stair rail near the CU.
I'd also made an effort to present nicely laid tails in the meter box and used IP65 Kopex pliable conduit to run a waterproof cable route from the external box up through the soffit. In the end, after he'd done a cursory polarity and earthing check, I got a compliment of having done a more decent job than he normally sees :)
Anyway, back to your point...
That approach, whilst watertight, might be too much effort for a CU swap without a full rewire - although it is highly advisable to actually run a full test on a CU change.
So, 3 other choices:
1) Get a sparky;
2) Do it and tell no-one. However, if you have to get the cutout fuse pulled, you might get grief from the supply company if you can't produce a decent story. Some modern meters have an isolator switch built in, it's not obvious, some sort of rotating arrangement in teh meter body rather than a big obvious switch. Some areas will fit a 100A isolator free or for a nominal charge. Siemens (meter operator) in London area I believe will, EDF, now sold to UK Power in the SEEBOARD area will not, ever. If you have a henley block to work too, it's not too bad live working, but I baulked at handling heavy wires with live ends as opposed to fixed down live terminals and wires with dead ends. Will be a hell of a big bang in your face if the live one touches anything earthy, no to mention electrocution risk.
Be aware that 3m is the typical max length for meter cables with most companies and some stipulate shorter. If you are exceeding that by much, the technical standard answer is to run the short tails into a 60/80/100A switchfuse (box with fuse and DP isolator). Make the fuse the same as or lower than the cutout fuse rating. The reason for this is that the supply company have strict limitations on what they deem their cutout fuse to be sufficient to protect and it normally protects the wiring from the cutout right up to the breaks in your CU.
In theory, it is possible to run such long or undersized meter tails that a dead short in the CU may not blow the cutout fuse before the tails suffer heat damage.
3) Find a friendly sparky who will let you sort the CU out, then he will come and test it all and handle the final connection.
3b) Part P it with 3rd party doing a test - more or less the same as 3).
If you aren't planning on selling the house anytime soon and don't really care about paperwork and think you are upto it, there will not be much likelhood of comeback for a DIY technical breach of building regs (failure to notify) as long as the job is sound. But if you choose to do this, I really would get a tester and read up on the testing procedure (I can outline the basics here if asked) - it's not difficult, but you'd need a copy of the Electricians Guide to the Wiring Regs to have the basic domestic tables of conforming numbers[1] to work to, otherwise your test readings will mean nothing.
[1] Things like max permitted Live-Earth loop impedances by cable size and breaker type being the main one that requires any degree of thinking. The rest of the tests are things like RCD trip times being in spec and a 500V insulation test of everything (without blowing up dimmers and stuff). Loop testing ring mains are a bit of an art as you do a figure of 8 test that makes perfect sense from a physics POV but is by no means obvious.
You'll need to understand concepts of earthing and bonding, but the uk-d-i-y wiki expalins that stuff well.
That's not complete, just to give you some idea of what you should do to do a by-the-book DIY job.
I suspect, based on what you've said, 3 or 3a will probably be the most suitable courses to consider and are perfectly practical, but in the case of 3, find the bloke before you start. Mate of a mate is the best bet - "foreign" sparkies will likely be scared by such a request out of the blue.
Cheers,
Tim
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Tim Watts

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On 22/12/2011 23:32, Stephen H wrote:

With tails that long you will probably need a switchfuse close to the meter.

I have done minor works and had BC accept my minor works cert (part of a larger job that need LABC oversight for other reasons). There are others here, who have also done notifiable stuff, with varying degrees of hassle depending on the BCO in question.
For notifiable stuff the procedure should in theory be the same, submit building notice, and let BCO signoff on the job when done. Make the BN woolly enough (like "rewire as required") and get it all covered by the one. However the reality is that many BCOs don't have the skills or confidence, or possibly LBA authority to sign off electrical work themselves, and may insist on you paying for an inspection - which starts to get silly. Others may have the authority, but actually lack the knowledge to sign off on correct work, and insist on it being done incorrectly instead (see recent thread on here regarding cooker circuits and BCOs!)
Personally I would probably phone the BC department and ask them how they do it in your area. Then you can elect to go the BN route if it sounds like they have a reasonable way of doing things, or make alternative arrangements if not.
(the alternative arrangement selected by 99% or more of technically competent folks being to simply ignore part P and get on with it - after all, what is going to happen?)

wouldn't dream of it ;-)
--
Cheers,

John.

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On 23/12/2011 00:14, John Rumm wrote:

Thank you Tim & John, you both have been very helpful.
I can give more detail on the work involved. basically the meter tails are currently 2m long from the white external meter cupboard to the old CU.
The old CU is the corner of what was the old double garage but is now a single garage and family room (one of the garage doors was bricked up and a window put in, and a dividing wall put in between the two garages)
The old CU and meter cupboard are essentially on the the same wall, the CU being on the internal surface and the meter cupboard on the external surface. The CU is 1m higher than the meter cupboard.
The new CU would go into the surviving garage, on the dividing wall so I am looking at 5 metres of meter-tail cable from old meter cabinet to new CU. This would be run via the dormer void (see later) and would run from the meter cabinet, over the family room ceiling and then down into the surviving single garage.
I am more than happy to uprate the meter tails cables to 35mm2 to deal with voltage drop due to the increased distance between meter and new CU.
I have no problem with replacing the 1.5mm2 cable from the nearest lighting roses to the new CU, ditto replacing the 2.5mm2 from the nearest sockets back to the new CU (avoiding junction boxes etc)
The cooker cable would be extended using those round suitably rated brown junction boxes. They would be accessible via a wall door in a dormer bedroom (which happens to be above the family room converted part of half of the double garage).
The immersion circuit will become redundant due to a impending combi-condensing boiler replacement. I was actually going to use this circuit as the new boiler circuit and down-rate the immmersion MCB to suit.
Can I get away with putting the switch fuse in the meter cupboard or is that against the regulations? SWMBO would not like having a switch-fuse in the family room as that's no better than leaving the the old CU alone.....
There is an alarm panel as well that needs moving but that's another story and obviously much easier to deal with from a part P perspective.
Regards,
Stephen.
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Stephen H wrote:

I would definately put a switchfuse in for that, near the meter, eg
http://www.tlc-direct.co.uk/Products/CGMSF100.html

That's where the elctricians guide to the 17th will be useful. That may not be necessary for another 3m.

No harm in well made junctions, eg crimp (wiht proper crimpers), DIN terminals or WAGO connectors (cable size permitting).
Your extended tails will not be RCD protected at 30mA so you cannot bury them, without resorting to armoured cable or metal trunking or conduit.
Visible runs are fine - I would use a bit of box trunking.

Here's what a highly respected poster here did (Andrew G):
http://www.cucumber.demon.co.uk/cu1.jpg

Technically, no. But it is often done. Depends if you need the supply company to be present. The meter reader (if you don't have remote readings) won't care.

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On 23/12/2011 01:42, Tim Watts wrote:

I wondered about that. Some galvanised metal trunking earthed back to the MET?
Well the new meter tail run would go from the meter cupboard upwards through the cavity (in the cavity wall) over the ceiling and joists for 2.5m As mentioned earlier, this is the eaves part of a dormer bedroom and I can make an access door in the plasterboard walls in dormer bedroom for access to this dormer eaves. Then the meter tails would go through a hole in the garage dividing wall and drop down a metre or so to new CU which will be at elbow hieght. (old CU requires a step ladder to access.)

I believe that in the meter cupboard, there is the DNO's fuse, then the Meter, then a double pole isolation switch. So that looks like I do not need to call in the DNO to disconnect old CU and connect up new CU.
Regards
Stephen.
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Stephen H wrote:

Hi,
OK, dissecting this:
1) Does the cavity or could the cavity contain insulation? Running unprotected PVC in cavities is frowned upon (though used to be done) as if someone fills that cavity with polystyrene insulation granules, you get a bad reaction with PVC cable insulation (specifically the plasticiser).
There's also a matter if derating cables. However, the cable is likely to be

RCD/mechanical protection. Overall, I would not do this. Can you not keep this on the surface, or is your meter cupboard flush mounted?
Failing that, can you get uPVC conduit down the cavity - this does not have a problem with polystyrene - no plasticiser - and will protect the cables).
2) The eaves space does not require any mechanical protection by the sounds of it, but personally I would.
Here's what I did in a similar situation (although my eaves are external):
https://plus.google.com/u/0/photos/104984236185710819272/albums/5646554496300833473
(Down the bottom)
3) The through-the wall, I would sleeve (even with 32mm PVC drain pipe) for the reasons mentions vis-a-vis cavity insulation. The final drop could be in PVC trunking as it is surface.
It's an awkward route and with the new requirements of the 17th, always a problem with tails as you don't have any RCD protection.
Can you not do a surface run up, in the corner of ceiling/wall then down in PVC trunking?
A photo or two at this point might be useful...
Cheers
Tim

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On 23/12/2011 08:47, Tim Watts wrote:

The previous owners put in cavity insulation 18 months ago.... But did not touch the loft insulation which is still at 4 inches(!)

Indeed.
The meter cupboard is flush mounted into the external wall. The CU is on the internal wall about 1 metre above said meter cupboard.

Is it acceptable to use UPVC flexible conduit that is about 5 metres long. put the meter tails and the earthing conductor through this conduit, run this conduit from the meter cupboard, through the cavity, over the ceiling joists in the eaves (across the family room ceiling) then through a single skin wall and then down to the new consumer unit? The single skin wall divides the two garages, the original one and the converted into a family room one.
Or have I got to use metal trunking?

See my question above about flexible plastic conduit.

https://plus.google.com/u/0/photos/104984236185710819272/albums/5646554496300833473
I see you do not have a switch fuse, which as I understand is compulsory if the meter tails exceed a certain distance. Will you be putting this switch fuse in the meter cupboard or does the DNO have to do this due to the live working issues involved?

Instead of a Switch fuse, could I not put in a 100A rated RCD switch in the meter cupboard? I will be of course having the standard 30mA RCDs in the new CU..
so to avoid tripping the whole house, I could make this 100A RCD a 100mA device so that the CU RCDs trips preferentially so taking out some circuits but not all of them. This would give some hopefully reasonable protection to the meter tails......
I am considering the RCBO per circuit approach as I will eventually have a wood burner which requires its own high integrity supply as if the pump stops, the WBS will vent steam through the header tank. There is also the smoke detectors and CO detectors which need its own MCB, and ditto the house alarm. Also the outside sockets i think should have its own RCBO so that it does not take out the rest of the house wall sockets with it.

SWMBO is the obstacle here

Agreed, will have to do this after Chrimbo.

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Stephen H wrote:

The only times you need mechanical protection are if running in the surface of a wall less than 50mm down from the surface.
Straight through is OK. If the cables go over the ceiling, but on top of the 4" rafters then there is little risk there. Some risk if it sits on the ceiling surface.
I would say that, by the sound of it, none of that route needs mechanical protection[1] and that uPVC flexi conduit in any form is sufficient protection for the tails in the cavity against any polystyrene that may be there.
You shoudl apply cable derating for the cavity run - sorry, I do not have my tables to hand to check if 25mm2 will be OK.
[1] I would wait and see if anyone else sees a problem (Adam, John, others?). Does the bit in the ceiling have a2nd storey floor over it (ie at risk from nails in floorboards)?
The Kopex pliable conduit I used (32mm) is damn tough (but not drill proof) and will take 2x 25mm2 and one earth - though you'd want to pre-assemble it straight, or at least get the bit down the cavity and glanded into the meter box leaving the rest straight whilst pushing cables. After that, the rest can be routed pre-stuffed. The Kopex is smooth bore which makes this easier, but it is not cheap (RS sell it) - about 40-50 quid for the minimum (5m IIRC) and fittings. It does not count as "mechanical protection" but offers a good deal of impact and abrasion resistance and even mice would have to be hard persistent bastards to bother with it.
If it is easy to get trunking over the ceiling, you could run plastic box trunking for the horizontal and gland pliable/flexible conduit into it at each end and possibly be cheaper and offer a little more protection.
It also means that the fiddly bit of stuffing heavy wires down bendy tube is limited to a short bit each end.

https://plus.google.com/u/0/photos/104984236185710819272/albums/5646554496300833473
No - my tails were witing the 3m max specified by EDF and the bloke was happy. He was a bit skeptical about the 100a wylex isolator I stuffed there, but let it go in the end.
Here's the finished job:
http://tinyurl.com/crbrvcg

No. You need to protect the tails against L-N shorts as well as L-E faults.
In practise the DNO's fuse would almost certainly manage, especicially as yours would have a similar characterisic (BS88 that most switchfuses have is not quite the same as their BS1361 (usually) cutout fuse but it's not that far different).
However, you would of course measure the supply impedance - or - assume it is 0.35 Ohm for a TN-C-S system or 0.8 Ohm max for a TN-S system (by law it must be and they can and must tell you which system you have),
then add in your caluculated extra resistance from your 5m tails, and if necessary, use a smaller fuse (eg 80A) or as you've suggested, heavier cables, to achive the correct disconnection time under a full short circuit at the far end (CU).

That would be the right device (well, 100mA Type S time delayed) if you had a dodgey earth (eg TT earth rod) but it does not protect against short circuits.

Good idea. I've done that, with a Hager CU.

I've trained mine that function trumps form if function = too difficult to do in any other way. But I understand...

Cool. I'm gpoing offline tomorrow for 3 days (cannot be tortured by work then, hehe)
If you want me to dig out my regs book, I can tell you the numbers (resistance of 25/35mm2 tails per m, disconection times, derating for cavity walls, BS88 fuse characteristics etc). It's kicking around somewhere here - but I won;t be able to find it until after Xmas too.
But have a lok at TLC's site - they have quite a lot of useful numbers there.
Have a good one!
Tim

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Tim Watts wrote:

I'll add: "in the scenario you described, as I think I understand it"
:)

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Tim Watts wrote:

Sorry I'm tired. Meant to add "but in this case, it's best to adhere to what they stipulate".
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