Old CU for shinney new RCB, MCB CU


Postby HeWhoWalksAmongUs » Tue May 26, 2009 12:01 pm

Is it possible to change over an old fuse wire type CU with a new CU with RCB and MCB switches?

It all works fine at the moment but I don't like having to ensure I have silly amounts of fuse wire and a torch hanging around and if it is a simple switch over it would make life a little easier.

The house has an isolation switch out side of the main CU so it is simple to isolate all the circuits.

Also does it matter if the CU has a number of blanks or unused MCB's?
I figure it is better to over engineer the solution than have to revisit everything for a minor change. (assuming Part P dont decide to force out current CU technology anytime soon)
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Postby kbrownie » Tue May 26, 2009 7:00 pm

Hi HeWhoWalksAmongUs
It is possible to replace old CU/fuse boxes with the new 17th edition types, with blanks to fill in the spares
It would be best done by a full scope electrician that is registered with a domestic intallers scheme or you would need to notify building controls which would charge a few of about £130.
Your installation would need electrical installation certs, schedules of inspection and test results. It is not really what I would consider a DIY job, the meters used to do the testing could cost between £200-1000.
Then they will also need to have a valid calibration certificate, which again could be an added cost of £40-60.
So, so far it's costing you at least £370 before you have removed and replaced CU, done any inspection and testing and filled in the relavent forms and you need all the tools to do the job too!
The electrician will do all that for you and likely to be cheaper and safer.
A good 17th edition CU, fully loaded. Could cost £60-100 if only a few circuits needed, electrician will recommend most suitable.
KB
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Postby sparx » Tue May 26, 2009 7:23 pm

Hi, it is of course better to have RCD/MCB's & blank ways should always be available, recommended 20%,
however since you mention it this is of course subject to part'P' rules,
regards Sparx
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Postby HeWhoWalksAmongUs » Wed May 27, 2009 8:50 am

Thanks, seems a simple job is now wrapped in a lot of expensive beurocracy. Spoken to a couple of industrial sparky mates and we are having real trouble understanding the use or Part P except as a union funded load of paperwork.

I am also wondering if it is possible to get any knowledge on how to go about new circuits. I have disucssed with sparkies and got most of my information about a new garage circuit from this forum (thank you all V.much) but it seems that since 17th everybody is now to scared to teach.
All books seem to have dried up and all advice seems to be just "call a part p sparky"

Thanks all to this forum.
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Postby HeWhoWalksAmongUs » Wed May 27, 2009 8:52 am

Can anyone suggest anything I should whatch out for with a new CU.
To me it would appear a simple job of taking the old wiring system and wiring into the new 17th CU. As long as I ensure the connections are good and the wires are in the right place. Is there any gottcha's to look out for?
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Postby kbrownie » Wed May 27, 2009 5:40 pm

HeWhoWalksAmongUs,
Ahhh!
Part P?
Could write an essay on the right and wrongs and how it should be governed and who it should concern!
If I did write an essay, I'd would summarises with the following:
It has it's place as far as safety is concerned with people who don't know what they are doing. Whether it should fly under the banner as it does or in another way, is another question!
CU's common problems are short tails to isolator in CU, circuit cables to short to reach MCBs and busbars.
Then any earth leakage faults currently on installation, that are not being detected as no RCDs installed yet! May trip new RCD!
Remember inspecting and testing correctly is not expensive beurocracy, it has to be done to ensure the system is healthy and safe.
Some people don't understand part p and that's fair enough, ask the question. The people that ignore it are the worry and the 17th eds has it's problems as did the 16th, 15th etc.. Lots of colleges and training centres doing courses on 17th eds and loads of books been upgraded to suit these courses, don't see anyone being scared of it just making more money!
KB
Last edited by kbrownie on Thu May 28, 2009 9:18 am, edited 1 time in total.
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Postby bd3cc » Wed May 27, 2009 8:54 pm

There is a myriad of things for your unit to comply.
Meter tails, earthing arrangement and size, testing.to name but a few,
Changing the CU is the least of the problems, complying with the regulations is the biggest.
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Postby moggy1968 » Thu May 28, 2009 12:09 am

if you just want to avoid changing fuse wire you can get MCBs which will plug into your existing fuse holders, of course this won't give you RCD protection and isn't upto 17th edition standards, but no reason why you can't do it as a temporary fix. as long as you don't change the spec of any circuits (by uprating the MCB for example) this is not notifiable either.
Andy
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Postby HeWhoWalksAmongUs » Fri May 29, 2009 8:54 am

Cheers for the replies, As payback for your help I have been lurking in your computers forum to offer advice.

I have checked my system and I will have to re-think. I have no isolation before or after the meter. No matter how much learning I can do I am not prepared to change a CU or add a switch from the meter tail while live.
I might build the new out door cuircuits I was planning and maybe call in a sparky to plug it in.
Just the price will be a little silly for the value I am placing on this new circuit.

Bizzarely the hardest part of all this is accessing the floorboards. Tongue and groove makes access very hard work.
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Postby kbrownie » Fri May 29, 2009 12:22 pm

If it's an outdoor circuit, It will still need to have an RCD to comply to BS7671:2008. We have already mentioned all the stuff regarding, Part P and electricians that are full scope part p registered, that all still applies.
I'd suggest if you intend doing this job yourself, to get an electrician on board before you start,
because if they are willing to and some won't be willing sign to it off for you when completed, they are then taking on a legal responsabillty!
If it was me signing it off I would be insisting that I oversee the work in progress.
KB
PS. Most of the people answering questions on this website are not connected to the website, we are just like you, registered users and offering free advise and information.
Added Later:
best method of accessing underfloor is to remove, T&G be using a circular saw, set blade at a depth of 18-20mm same as T&G cut along where T&G is fixed to joist avoiding nails and screws remove prior if possible. Then run saw down the length of the joint of both sides where they join with next length in row and you will be able to prise up then without causing damage to floor. Be careful to look out for pipework and cables when cutting (not that easy as you are cutting from above but be aware) thats why you must set depth of blade as small as needed, there should not be any at that depth but don't rule out the idiot factor of the person(s) that may have installed them.

Hope helpful!
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