Make Up Of Consumer Unit

[Grinning Grandad]

I am one of these much maligned people who have just completed a 'part p' course. However I don't think for one moment I am in any way remotely qualified to call myself an 'electrician'. I have always been competent in DIY electrics and after a mid-life crisis wanted to have one last career change before I get too old. I have the 2381 and EAL qualification so can apply to join a scheme if so wish (after some work under my belt). I have taken a 2391 exam but won't pass (and don't deserve too) but I passed the practical so know about the Inspection & testing. I also own a Megger 1552 and have spent hours practicising at home.
Anyhow, I have been asked to replace an old fusebox for a new CU. I have informed the Building Control and the Supply company are coming to fit an isolator. The reason for posting is really to ask for some opinion on the make-up of the new CU.
Its a bungalow and the current fuse box is 4 way. After checking, only 2 are in use 30A Ring and 5A Light. There isn't much room in the cupboard for a new CU (9" at most).
It would be easy to install a new CU for the 2 circuits but I want to leave room for expansion because they will want a re-wire in the future. Apart from the 2 there at present I think leaving room for another ring main (kitchen), Shower (they have already asked me to allow for this), and possibly Cooker (its gas at moment but you never know). So thats a total of 5, 3 of which will want RCD protection (but only one for now). Bearing in mind the limited space I was wondering how other people would 'build' their CU. Its not really a major problem because if I have to I could dismantle the cupboard and buy a ready made split load from Screwfix but considering the small number of current (and potential) circuits I was simpy wondering if anyone would do it different.

 

[JohnD]

if there are few circuits and little space, consider the use of RCBOs. Depending on make they need by no wider than an MCB, and will save you have to put in an RCD as you would in a split-load, which takes up two positions or more.

If there is only one socket circuit at the moment (which isn't much) the cost should be similar to a split-load with RCD.

It may be that you are accepting an unreasonable size constraint. 9" is very small; even a bungalow will (sooner or later) need, in addition to 1 x lights and 1 x sockets, 1 x cooker and 1 x garden circuit. There is a lot to be said for 1 x Freezer (non RCD) and 1 x Alarm) non RCD and unless they have a combi, 1 x Immersion or 1 x shower as well.

The pattern of adding on more and more small CUs of assorted brands and quality because there were no spare ways in the original is undesirable, as well as being extra work and expense.

BTW if they are having to pay for BCO inspection and test, it might be worth doing the kitchen at the same time to save later cost. Also, if you have a 20A radial serving a single socket in the cupboard, and a 6A lighting circuit also serving the cupboard (these can be very useful working circuits), it is possible to add extra sockets or lights to these circuits later, which in most circumstances is not notifiable.

 

[Grinning Grandad]

Thanks for that John, I have seen a 5 way consumer unit that will fit but the RCBO's are pretty expensive, though as they only want one for now its not too bad. I will give the customer the choice of small restricted CU with RCBO or making the cupboard bigger. (Incidentally a larger CU won't fit on the wooden board that all the hardware sits on - there is nothing stopping me adding an extra block of wood to the side to make it larger is there?).

Thanks also for the tip regarding the single socket and light circuits. Will save a lot of paperwork & money.

 

[JohnD]

If you have a backboard, no prob, fit a new one. If it's got the meter and/or cutout on it, it belongs to the distribution co, and they are entitled to remove it at whim, so they don't like customer's equipment on it. you are allowed to fit Henleys and an earth block if you want, but IMO it is better to put all customer equipment on your own board. I like white Laminated Chipboard (as used for kitchen worktops), it is easy to wipe clean and the surface is flameproof. As it is very hard you have to pilot drill for all screws.

It is easier to fit the new one before you decommission the old one, unless you are sure you can finish the whole job in less than a day.

If you like to use a backboard, space it off the wall by 35 to 50mm, using wooden battens. then you can lead all the cables in through the back without needing any knockouts or sawing the cover, looks very neat.

Some people say backboards are old fashioned

 

[ban-all-sheds]

Indeed they are not, for the reasons you say.

Not sure about using kitchen worktop material though - 30mm thick, minimum?

 

[JohnD]

you can also get 16mm laminated chipboard, but the cheap stuff is vinyl foiled, didn't want to get into that.

 

[Dippy]

they will want a re-wire in the future.

Out of interest did you discuss this? Even with your best attempt at leaving them with future capacity it might not be enough or might not help with the new BS (17th ed). If their future plans need more that you can provide then they'll be better off by biting the bullet now and moving the CU to where there is more space?

(P.S. this is just personal opinion and not professional advice).

 

[Grinning Grandad]

Posted: Wed Jan 09, 2008 2:31 pm Post Subject: Re: Make Up Of Consumer Unit

--------------------------------------------------------------------------------




Out of interest did you discuss this?

Yes I discussed this at the time but they wanted to split the job for financial reasons. After reading all the advice I have decided that a larger CU with some spare ways is the best solution. I will just have to put my woodworking skills to use regarding the dismantled cupboard.

Thanks for the advice