DIY Doctor

installing new CU and new garage CU

Postby paultoolbox » Mon Jun 29, 2020 10:56 pm

hello all
i may start some work this week can you take a look at photo`s of this new unit and my old unit i`m about to install
this unit from screwfix
also wanting to install a 63A MCB from this new unit to a garage unit with 16mm twin & earth cable
i`m having a problem finding a garage unit which will accommodate 2 x 32A MCB and 1 x6A mcb
reading up about RCBOs would it be better to use these in the garage unit
thank you all
old unit 2.jpg
old unit 1.jpg
consumer unit2.png
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Simply Build It

Postby ericmark » Tue Jun 30, 2020 1:11 am

Looking at Screwfix website largest RCBO is 40 amp, type AC curve B 30 mA. I can't see any 63A RCBO's. And even with MCB largest is 50 amp. It says high integrity board, but would check on that, looking at British General CFDP16610 on other sellers web sites it does not say high integrity, what high integrity means is there are three neutral bars, so you have some MCB's on one RCD, some MCB's on other RCD, and also either MCB or RCBO which does not go through many RCD's so you can run steel wire armoured cable without RCD protection to a second consumer unit in your garage and that consumer unit will have the RCD for the garage.

One RCD could be removed in the main consumer unit, and RCBO's fitted in that side, but at £24 each that gets expensive, I paid £10 each for my RCBO's and still my consumer unit cost around £250 with surge protection and external isolator, a tad more expensive to the £68 you have paid. It was slightly bigger 18 module so with 2 for isolator and 2 for surge protection that left 14 RCBO's.

I made a mistake, I saw type B and thought the RCD built into the RCBO was type B but it referred to the tripping curve of the MCB portion of the RCBO and the RCD is type AC, not really what I wanted as I have some inverter powered equipment. Really needed type A.

So you could remove the RCD on one side and fit RCBO's maybe 3 RCBO's one for each ring final, and one MCB to feed garage, that's £72, then three RCBO's in garage another £72 plus the consumer unit, it starts to add up.

I went to local supplier (Link) and got a cheap CP (Electric) Limited board, as said £10 each for the RCBO's and they are available at 50 amp, I think price was before VAT can't remember exact price but under £250 and over £200 and included other bits like crimp pliers, cable, and external isolator.

The last house before we moved here had two RCD's feeding two fuse boxes, and from time to time they would trip for no apparent reason, it seemed to come as a batch with maybe two years between them, it was fitted late 90's so have had RCD protection for a long time, but over that time we have lost a few freezers full of food, so this time went all RCBO. One reason was lights split up/down and sockets split front/back so there is no way with just two RCD's that I could ensure lights and sockets in every room are on separate RCD's. And must have cost over £200 loosing two freezers full of food. Clearly did right thing as a roof leak did cause a RCBO to trip, but I could do without that circuit so no problem.

With the old dorman smith loadmaster I remember 70 amp MCB's, but not seen any over 50 amp with today's DIN rail mounted MCB's. As to if RCD in garage consumer unit or house consumer unit, both have plus and minus points, but with twin and earth not really any option, needs to be in house. Personally I would run SWA to garage unless integral.
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Postby Mr White » Tue Jun 30, 2020 11:26 am

paultoolbox wrote:hello all
i may start some work this week can you take a look at photo`s of this new unit and my old unit i`m about to install

Often when doing a job like this it is best to get the electrician who is going to do the job first, not the other way round. That way he can test it all and issue a certificate, as without it can cause problems in the future.
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Postby paultoolbox » Wed Jul 01, 2020 1:11 am

thank you both for your kind reply's
ericmark wow i like you already !!!!
to think you had the time to write all that and explains things
thank you
would you have time to look at which main consumer box would be suitable for my needs and a garage cu
my local wholesalers close to me are below ?

ericmark i`m a retired builder but still very active packed in building 30 years ago went into fitting kitchens and bathrooms
i have re-run countless cables in the past so i know the dangers of electrics also replaced a few consumer units i have no worry s about replacing the old CU but the new CU
if you agree would require a 63a MCB to the garage CU run with 16mm twin and earth ?
i just need advice what to buy got SWA cable 1.5mm & 2.5mm
all for the outside as i say looking into a good MAIN CU UNIT
and a ( garage CU which i`m installing at rear of house )
as i want to control all lights from my house 8 fence lights 60w
also a lamp post and a pillar light also 1x 100w flood light
also a 4 outside outside sockets
i have plenty off free time as i would like to carry out this work
if needs be at end get someone to to test all !
thank you
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Postby ericmark » Wed Jul 01, 2020 10:39 am

The cost to DIY a new CU legally is prohibitive, in theory you can still do it, but in real terms the system would only work with an electrician working in his own home. The LABC inspector or in England a third party inspector has to satisfy themselves you have the skill. And the LABC in Wales don't know English charge £100 plus vat for the first £2000 worth of work, so doing a complete rewire may be worth DIY, but small jobs you pay the inspector more than it would cost to get a scheme member to do the job.

In England you can have third party inspectors, but most the schemes simply will not allow it, and where it is allowed it is really an in-house thing so an electrician in a firm can sign off a plumbers work.

Also if the LABC inspector feels it is beyond his skill, he can appoint some one else to test it, and charge you his fee. This is what the LABC inspector wanted to do with my son and I when we took over a job in my mothers house. He would not accept my sons C&G2391 inspection and testing qualification, so my son said fair enough, but the guy you use must clearly be higher qualified than us, my dad has an electrical degree, only then did he back down and say we could do the whole job our selves.

When you sell or rent the house you will need a compliance or completion certificate, to be frank it's a tax, when I came to sell mothers house I could not find the certificates, so applied for replacements, I was told it would take 4 months, and it would cost how ever long it took them to find them, at so much per hour, clearly by that time house would be sold, it seems you can get insurance to cover any faults found when paperwork missing, but I then found the originals.

The paperwork was really useless, as it does not identify the installation certificate it refers to, so you could rewire a whole house and say the completion certificate related to that, when it only related to a kitchen socket. So it is all a trust thing anyway, however clearly doing that is fraud.

Changing a CU by the book is a problem even for electricians, we are officially not allowed to draw the main fuse, so it should be a case of fit an external isolator first, then get the DNO to wire it up, and then you can turn off power, how upset the DNO gets varies area to area, and in some areas they turn a blind eye to seals being broken when they see a new CU, technically I think the DNO should provide an isolator, but two wrongs don't make a right.

Problem with DIY is the DNO can think you have been stealing power, and with the new smart meters they are sent a message when power is lost, so they know you have drawn the fuse and for how long.

You want paperwork from a scheme member electrician that says they fitted the CU so you can show the DNO it wasn't me honest Sir.

If you use the LABC route, then they will insist it is done by the book, I could have simply said your not allowed to DIY fit a CU but technically that's not correct, but in real terms it's not easy.

Once you get an electrician who is a scheme member to do it, he will have a trade account with some whole sale outlet so can by it cheaper than you.

However you can clearly still fit the garage one, it would not be legal but unlikely to get caught, and you could always remove it before selling or renting house, and no one seems to worry anyway.

So now down to nitty gritty, how much power do you need in the garage? We will look at three stages.
1) 13A or less, all it needs is a fused connection unit FCU, no need for a CU.
2) 50A or less, depends on house CU what the largest MCB/RCBO is but it can come from the CU.
3) Over 50A in which case a henley block is used and wiring to shed has to be able to take the full 100A of the DNO fuse.
A property under the control of an ordinary person should use type tested electrical equipment, which means although you can get a moulded breaker any size you want, you can't use them in the home as not type tested, well officially anyway. At around £95 without the enclosure the normally would be to fit a fuse like the one the DNO use.

Anyway you need to work out how much power you really need, if the electrician fits a 63 amp socket which you say is for a welder which needs a 45 amp supply and once he has gone you fit a blank and use it to terminate the SWA into then you have not made a new circuit, so in England have not broken the law. If you simply get him to fit a 45 amp RCBO ready great but I don't want to know your breaking the law, or anyone else on the forum, breaking the speed limit is something we all I am sure do, but posting a video on U Tube of you doing it is crazy, yet people do.

So really next is the cost of materials v chance of trip, I used an all RCBO board here, no way after last house do I want to lose a freezer full of food because some water gets into an outside light. My son is an electrician as well as me, so I was lucky he fitted it for me, but if he wasn't then I would have got a scheme member electrician to do it for me, so paper work all correct, at 69 year old at some time in the future it is likely either my wife or I will need home help, so health and safety at work comes into play, so all needs to be legal. Had same problem with mothers house, cost a fortune to get it rewired, but had to be legal so if mother went into a care home, we could rent out the house.

But when my son was going to fit a CU for me, I went into Link the local whole sale outlet and say what have you got, in hind sight I made an error as the RCBO are type AC and really should have been type A, but not really that worried, they still trip if some thing gets wet, I saw type B on the box and thought great, but it turned out it was tripping curve B the logo on the RCBO shows them to be type AC and there was nothing on the box or paperwork to say type AC just a small logo on the RCBO.

As to how many electricians really look unless installing outlet for an electric vehicle I don't know? As said it was only after they were fitted I thought oh I have inverter drive washing machine, freezer and fridge freezer should have been type A not AC.
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Postby paultoolbox » Thu Jul 02, 2020 12:49 am

thank you ericmark
i understand what your saying
but i only want to install a better CU that is there now
if you look at my cu i have a isolating switch under CU
i would not need to draw the main fuse
ideally i would love to get rid of all those card meters
they are not needed any more i pay by direct debit
can you take a look at my plan hope the image works
i`ve taken out some sockets as perhaps are not needed
would these work comfortable with no overloading from a garage CU
as i would doubt that all sockets would not be used at the same time ?
would you say that the 63A MCB at main CU is to big and perhaps a 50A MCB would work
if the lighting to to big to work of 1 6A MCB i could install 2 6A MCB`S ?
1 for the fence lights the other for the flood light ?

i was going to run 2 x 2.5mm swa cable 1 direct to the shed just to add a light and a double socket i will not be drawing a lot of power from shed just the light and use sockets to charge phone or radio ( NO power tools ect,)
cable 2 was to power water feature and other 4 sockets

i do not wish to nag you your final word i will have to accept
what would be the point if connecting all the sockets outside and lighting and the garage CU
then get an electrician in to replace the main CU
would he then check my work oh be sarcastic
i say i`m not checking that ! so i`ll be at no ends
thank you again for your advice
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