separate consumer unit for extension

[BuildingNovice]

We have built a rear single storey extension.

The builder's original spec was to provide a new 7 way high integrity consumer unit, my understanding being this would replace the existing unit for the whole property.

Now, well into the build, he says that if he does as above, then we will need the existing house electricals tested and if found defective, we will need to fix before building control provide completion certificate.

He therefore suggests installing a second separate consumer unit to solely supply the extension (placing it next to the existing unit in the house), thus building control will only need to certify this.

Is there any problems with having 2 consumer units?

I will be grateful for any comments whether he is saying this to avoid genuine further costs (would have been helpful if he had clarified this at the start), or if he is cutting corners.

 

[Taylortwocities]

That is quite a normal way of going about things.

At the main supply end he will need to check and upgrade the earthing conductors but would not need to test any of the existing circuits.
The additional board then is used to serve the new extension as it does not impact the existing.

BUT -
CAUTIONARY NOTE

All new electrical work must comply with the 17th Edition of Wiring Regulations (BS7671). For most houses this means that all circuits would need to be protected by an RCD.

What this means is that if you are planning any future electrical works in the existing house then you may need a new consumer unit so that the electrical works comply with the regs.

So it may be as well to bite the bullet and get it done now.

 

[Adam_151]

Bearing in mind building control works differently in Scotland than it does in England and Wales, and I don't know much about the scottish system... so I'll try to not tie that in too much ane leave the in and outs of that to someone else

But if the work is being done by a competant electrician to BS7671:2008 (17th edition regulations) and he correctly issues an EIC for his work then I can't see the building officer having a problem

So that said, as you are subtsantially adding to the installation, then the supply tails, earthing and bonding need to be upto scratch regardless of whether a separate DB is installed or not.

Replacing the existing DB could cause issues, there could be issues such as borrowed neutrals and low insulation resistances which could mean RCDs could trip out, these would have to be fixed first... but I wouldn't say everyhing that is wrong with them needs to be repaired to change the DB, just anything that will cause new DB to trip out or is immediatly dangerous, anything else could be noted on the cert (just as it should be if it was noticed while fitting s separate DB...), the actual testing of existing circuits as part of a board change should not take that long... how many circuits do you have? (and what size is the existing house)

And I'd recommend you to have the whole board changed, ideally to one with plenty of spare ways, I've done jobs where a job ended up with three DBs because over the years people did different work and tagged DBs on to supply their bit, it ended up a right mess... the solution of course was to rip it all out and put in a new board to cover it all (which is ideally what should have been done 7 or 8 years ago when the most recent extra DB was added, but for whatever reason it didn't!_

 

[BuildingNovice]

Taylortwocities,

Thanks for your response.

I think 2 separate units may be an advantage as one tripping/malfunctioning should not affect the other?

I hear what you say about replacing the existing CU in the future, but presumably that only applies if the wiring is redone. For example, simply replacing light fittings (e.g. recessed downlights to ceiling spotlights) is not notifiable and would not need a new CU.

 

[BuildingNovice]

Adam_151,

Thanks for your reply too.

In fact, we moved to London so its the English regs in issue.

We currently have 7 circuits set up in the CU, and house is an average size semi detached with a rear 50m2 extension.

I think the second CU will probably use up all 7 circuits - if we need more in the future, I can always replace the existing CU with a larger one?

Apart from perhaps a slightly higher overall cost, compensated by part being payable in the future, I can't see any other downside of having a second CU fitted now?

 

[PrinceofDarkness]

BuildingNovice: A second CU is often the preferred choice of an installer when wiring extensions. That way, he is only responsible for the new wiring connected to that CU (apart from checking that the existing installation is capable of expansion). But it's very often a matter of convenience for the installer, in that he can turn a blind eye to your existing installation.

It's a pity that your 'builder' didn't send his electrician round, at the early stage, to explain your options.

You haven't indicated the age and condition of your existing wiring. There's nothing to prevent you getting independent advice from a trusted electrician to ease your mind.

My feeling is that there's no 'problem' with having a second (or third, for that matter) CU. It depends upon whether you want to keep all your eggs in one basket, or not........



Lucia.

 

[baldelectrician]

I would steer clear of additional consumer units

You could replace the existing consumer unit and have it tested at the time.

If there are any faults in the existing it would be noted on he cert.

The electrician could issue 2 electrical installation certificates - one for the consumer unit change and one for the new extension.

I would reccomed using RCBO's for the extension circuits on the new consumer unit[/url]

I would suggest you use Hager (or MK) consumer units. Wylex have just had a product recall (burning issues)

ps
As you are in Scotland -
You should use a competent person for the work, links below
In Scotland:
Individuals registered;
http://www.sbsa.gov.uk/register/ListAC.asp
Companies
http://www.sbsa.gov.uk/register/SearchRegCo.asp?T=Construction

 

[JohnnyG]

ps
He's not in Scotland now, see above post.

 

[GaryMo]

The electrician could issue 2 electrical installation certificates - one for the consumer unit change and one for the new extension.

Why not one to cover all the work?

 

[BuildingNovice]

PrinceofDarkness,

Thanks for your response.

My understanding is the existing wiring is probably about 15 years old (house was rewired in late 90s).

It's not so much I am worried about existing wiring, just need to be clear on pros and cons of 2 CUs.

Do you mean having 1 CU is having all eggs in one basket? Are 2 CUs therefore better for some reason?

 

[BuildingNovice]

baldelectrician,

Thanks also for your response.

Please could you briefly explain why you would steer clear of additional CUs - what are the problems as you see them?

Also, what types of faults would prevent an issue of a B regs cert as opposed to just being noted (and what does this mean - are you under an oligation to recitfy in a certain timescale?)

Thanks for your recommendations - much appreciated.

 

[PrinceofDarkness]

BuildingNovice: I can only reiterate my previous post by saying that it's often a soft option for the installer to fit a second CU, because the doing of it only makes him responsible for his own additions and extensions. There's nothing wrong in having a second CU - provided it's installed correctly as an independent unit.

If the switchgear is tucked away in a cupboard, or otherwise 'out of sight' then there's a lot to be said for an additional CU. But if it's in a prominent position. then you might opt for a single, larger unit.


Lucia.

 

[baldelectrician]

Additional CU's tend to be of the cheap and nasty type.
They then mean you will have an isolator switch in each unit- could lead to confustion if somoene is doing DIY in future times

The reason for 2 certs (if there are issues found when chsnging the old CU) means you get a 'clean' one for building control - the warrant covers the extension so they are only really interested in the extension electrics - as far as the electrics goes.

Any EXISITING faults should not make building standards concerned as they will be interested in the new bit

The builder seems to be trying to railroad you in to an easy life for his electrician.

I would sstill suggest RCBO's for the new stuff as this means the new stuff is completely seperate from the old stuff

ps
I would suggest you check the electrician out on the links I set out below

 

[GaryMo]

Additional CU's tend to be of the cheap and nasty type.

That's a very sweeping statement and not always true.

The reason for 2 certs (if there are issues found when chsnging the old CU) means you get a 'clean' one for building control - the warrant covers the extension so they are only really interested in the extension electrics - as far as the electrics goes.

There shouldn't be a 'clean' certificate and a 'dirty' certificate.

Prior to changing a consumer unit it's advised to carry out a Periodic Inspection Report. Any observations and recommendations would be noted there. You can then have a chat with the client and discuss what needs to be done to bring the installation to a satisfactory standard.
When that's been done then you can go ahead and change the consumer unit without any issues being found or listed on an EIC.