Planning new consumer unit. Is this design ok and should I even be doing it?

Hi,
I've just bought an ex-council house, built in the sixties, that needs rewiring from top to toe. As I don't have the three thousand pounds or so required to do it all in one go, I was going to stick in a new CU for now and start replacing/adding new circuits as I go. The current fusebox has 4 circuits. One for the sockets, one for the lights, one for the cooker (which I think is actually powering the kitchen sockets!) and another one I'm not sure about. There is also a separate fuse for the shower.
What I was going to do was to pull the fuse out of the incoming live feed, as the tails from the meter go to an unswitched junction box and thence to the main board and the shower board, and then disconnect the tails connecting the junction box to the old main board and attach them to the new CU. Actually, maybe I'd be better attaching them to a Henley switch and then to the new CU. The main fuse does have a wire seal on it and a torn paper seal that states it is illegal to tamper with the equipment. I've read a lot of posts about people just removing the main fuse, so what exactly is the legal situation.
So, I've come up with the following split layout for the new CU. I reckon I'll need the following circuits, the first part will be on the RCD protected circuit, the second part on normal MCBs :
* Sockets - Downstairs * Sockets - Upstairs (including loft) * Sockets - Kitchen * Cooker Extractor Hood ========* Lighting - Downstairs * Lighting - Upstairs * Fridge/Freezer * Gas Boiler Electrics * Cooker
* Shower will stay on the separate board.
I'm not sure if I really need the cooker hood or the boiler electrics on separate circuits. What is the general opinion on this and also of the overall layout?
If I go ahead and do the actual wiring for the sockets and the lights, but not the kitchen and bathroom, will I need to declare under part 'P' or would the separation of the current socket and lighting circuits into upstairs and downstairs circuits constitute replacement rather than new work? How likely am I to find a suitably qualified electrican who would be prepared to certify any work I did?
TIA, Organoman.
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Organoman wrote:

Bring shower onto new CU and ditch separate board; looks messy.
Add a cooker circuit, you may not need it now but a future occupant may thank you.
Immersion heater circuit?
Add interlinked smoke alarms at the same time as doing the wiring.

Both can go as fused spurs off a ring. You might want to do the boiler as a FCU on the fridge/freezer radial circuit, then you don't lose heating if the RCD trips.

IMHO it will class as new work; a new CU will definately class as new work

Unlikely, because they would be taking responsibility for your design calculations and hidden wiring, which they cannot see, as though they had done the work themselves.
Owain
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Organoman wrote:

Technically illegal (not your property) but Health & Safety legislation is probably on your side. ie. them exerting their rights of ownership over the fuse seal would jepordise your safety as it would encourage you to work live. Anyway, no-one cares - just do it.

I would remove the extractor - fused spur from kitchen sockets. And add the shower to the RCD protected side of the main CU for neatness. I would do as you have done for the boiler - also add the immersion to the same cct.

If you're getting a building notice anyway then worth declaring I reckon - you'll have to fight your BCO to see who will pay for inspection/testing - it shoudl be paid for by the BC office. I did my own which the BCO is happy with. In fact, if it was me, I'd do all the inspection/testing myself anyway (hire the equipment) just as a final check that all is OK. Then you have the paperwork should it ever be required. If you get a good book out of the library - or buy one - then testing/inspection is not difficult if you are confident with 16thEd regs anyway.
Jon.
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Tournifreak wrote: <snip>

<snip>
Hi,
Thanks for the detailed reply. I had considered putting the Shower into the CU, but was concerned that it would exceed the 100A limit on the CU as the cooker is already on it. The seperate shower box would be changed to an RCD/RCBO at the same time, unless you reckon that having the shower and the cooker in the same CU would be acceptable.
Thanks, Colin.
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Organoman wrote:

Wouldn't it also exceed the 100A limit on your incoming fuse?!? (Unless you have an unusually meaty power supply!) I would expect diversity will ensure that >100A is never drawn for very long. After all, the shower will only be on for a few minutes at a time, and your cooker will turn on and off with its thermostats - and how often does anyone use all the rings and both ovens together at full blast?
Someone else may have a better answer though...
Jon.
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Tournifreak wrote:

Well as you say, the incoming fuse will most likely be <0A, so as long as the main CU switch can handle 100A then it is protected by the main fuse
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Richard Conway wrote: <snip>

They're both fair points. It did occur to me afterwards that it is unlikely I'd be cooking whlst having a shower too :-) Single CU it is then, with the shower on the RCD side.
Thanks muchly, Colin.
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On Wed, 15 Mar 2006 10:19:15 GMT someone who may be Organoman

The cooker hood may as well be on the ring main (or indeed lighting circuit, whichever is easiest), rather then running a separate circuit for it. They are hardly vital bits of equipment.
Having the boiler on a separate circuit means that faults in the general power circuits don't affect the boiler. A good idea.

What rating of protective device for the cooker and shower? What rating is the main fuse? In most circumstances having both on the same board is fine, there will be a great deal of diversity.
I would also consider a separate circuit for an immersion heater, to provide emergency water heating (and perhaps summer water heating), though depending on layout this might be combined with the boiler circuit without too many potential problems.
Don't be tempted to use a cooker control unit with built in socket. This tends to increase the size of the cable and protective device. The socket may not be in a very clever place either. These things are a throwback to ye olden days when sockets were rare things. It is far better to provide sockets from the ring main.
--
David Hansen, Edinburgh
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Organoman wrote:

Please do be very careful with the service head. There have been reported cases of ye olde oil-impregnated paper insulated cables becoming dry (oil drains down) and failing catastrophically when disturbed. Rare, but read on...
The next fuse up the line from yours is likely minimum 300A, if it's in a link box in the pavement - potential fault currents at the service head are very large numbers (many kA upwards). A short on the incoming cable causes the sort of bang and flash that sets stuff on fire, including you.
If you're not certain, can you take a picture and post it somewhere?
If it's newish looking PVC SWA then it's probably a safer bet. Obviously isolate all your load before pulling the fuse.
If the cable is lead sheathed or wrapped in self-amalgamating tape, it may be old school cable and possibly deteriorated.
Your best bet, to be sure, is to phone your REC (not the people you buy electricity from, but the people who actually run the LV network), and ask them to come and fit a 100A isolator. Some do it for free - and you'll be able to isolate whenever you like.
HTH
Tim
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Tim S wrote: <snip>

<snip>
Hi Tim,
Here's a picture I took of the unit a couple of days ago, the first one is a lo-res version (379KB) and the second is a hi-res version (1.8MB).
http://www.organoman.co.uk/misc/fusebox.jpg
http://www.organoman.co.uk/misc/fusebox-hi.jpg
The white cable is actually black, it's been painted over.
Cheers, Colin.
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Organoman wrote:

Hi
The main cable looks extremely old at first sight, though obviously the meter and associated tails are new.
That's the sort of service cable I personally would be wary of touching.
If you really want to pull the company fuse, make sure the service head box is still firmly screwed to the backing board so that you can be sure that the cable won't be disturbed when you do pull. The risk isn't *that* high, it's only if you do draw the short straw, the booby prize is likely to be a visit to hospital.
I'm not normally known for being wufty, but I'd be calling the REC and asking them to come and fit an isolator, if it were me.
I've got to run to work, I might make some comment later if I think of anything.
Cheers
Tim
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