Do I need to replace the whole of the consumer unit?

[Zehroni]

I need to wire the newly built extension. the lighting of the extension will be connected to the existing house lighting circuit. However, the power sockets will be on a separate breaker run all the way from the consumer unit (the board). Do I need to replace the whole board or just RCD the newly added breaker for the extension?

 

[winston1]

No need to replace the whole CU.

 

[ericmark]

BS7671 is not law, however a new circuit is notifiable, so it is up to LABC what they will permit. If done by a scheme member he has no real option, he has to follow the current BS7671 Before 2018 when we went to metal then it may have been possible to fit a RCBO .

 

[Risteard]

We "went to metal" on 1/1/2016.

 

[John D v2.0]

I don't see why it wouldn't be possible to fit an rcbo even now, assuming one is available. Otherwise a separate RCD in an enclosure would be alright, sometimes done for showers.
The extension to the lighting circuit may also need RCD protection if the new cables go along walls etc.

 

[JohnD]

Show us a photo of your CU please, with the door open.

 

[ericmark]

I don't see why it wouldn't be possible to fit an rcbo even now, assuming one is available. Otherwise a separate RCD in an enclosure would be alright, sometimes done for showers.
The extension to the lighting circuit may also need RCD protection if the new cables go along walls etc.

I would agree, however it is not what @Zehroni is willing to do, but what the person who is raising the completion or complacence certificate is willing to accept. In my old house still have an adaptable box with two RCD's and two old Wilex fuse boxes supplied from them with MCB's fitted instead of the fuses, one plastic and one plastic and wood base, it would not strictly comply as non of the units are type tested, although since I am not an ordinary person that does not matter, and they are not flame resistance however since fitted in the garage where there is nothing to burn that does not matter.

However I am not doing major electrical work in the house, and so not looking at anything which will require a completion or complacence certificate, with a

newly built extension

it is unlikely the work in some way does not need a completion or complacence certificate, likely both, and if one knows the LABC inspector is likely to visit if I was a scheme member electrician I would not want to do anything which he may pick up on, however I do wonder if the LABC inspectors walk around with their eyes closed, as the one inspecting this house allowed the fuse box to be located between ceiling and flat roof with a 9" square hole in ceiling which one could stick ones hand through to just about replace fuses.

So yes a mini consumer unit with a RCBO would do the job, but one is it worth it, and two will an inspector accept it?

Note:- A consumer unit is a type tested distribution unit for use when an ordinary person is in control.

So Screwfix prices a 5 module consumer unit (garage or shower) is £29.99 and a 12 module consumer unit is £31.99 so the cost of parts is nothing really (both unpopulated) where the cost comes in is paying some one so you get a completion or complacence certificate be it the LABC inspector or a scheme member electrician, last time I came to do electrical work needing a completion certificate the LABC charge was over £200 and they wanted me to employ some one else as well to inspect after, after some talking they did in the end agree I could complete the installation certificate, but unless you can show you have the skill it will likely cost around £300 using the LABC route to do latter, and around the same using a scheme member electrician, so may as well fit whole consumer unit rather than a mini one as so little difference in cost now, and it will cost so much to change latter.

The LABC inspection is paid for in bands, depending on cost of work, lowest band is £2000 so that's why so expensive latter. It is not safety or electrical regulations (BS7671) I am thinking about, it is the cost of the paperwork if done latter.

 

[SUNRAY]

So Screwfix prices a 5 module consumer unit (garage or shower) is £29.99 and a 12 module consumer unit is £31.99 so the cost of parts is nothing really (both unpopulated) where the cost comes in is paying some one so you get a completion or complacence certificate be it the LABC inspector or a scheme member electrician, last time I came to do electrical work needing a completion certificate the LABC charge was over £200 and they wanted me to employ some one else as well to inspect after, after some talking they did in the end agree I could complete the installation certificate, but unless you can show you have the skill it will likely cost around £300 using the LABC route to do latter, and around the same using a scheme member electrician, so may as well fit whole consumer unit rather than a mini one as so little difference in cost now, and it will cost so much to change latter.

This is something that sooo many poeple don't get and I've seen so many situations where the cost of a Henly block and extra tails etc has exceeded the cost of a better CU. I encountered one a short while ago in a fairly new house with a stupidly small CU and as part of the 'new build' the buyer had paid for a shower circuit and a feed for a shed, both had been installed using 4 way CU each which matched the main 12w unit but randomly positioned around the under stairs cupboard. An 18x CU would have been cheaper than 2x 4w's, tails, Henly block and earth bar, a bonus is the 12w would have been usable elsewhere on the developement if it had already been fitted. The time taken should have been quicker too as this was ordered before ground break.

 

[SUNRAY]

I need to wire the newly built extension. the lighting of the extension will be connected to the existing house lighting circuit. However, the power sockets will be on a separate breaker run all the way from the consumer unit (the board). Do I need to replace the whole board or just RCD the newly added breaker for the extension?

This really is a question for your electrician, before any serious advice can be given here we need more info. Let's have a pic, as John has asked.

 

[Risteard]

I don't see why it wouldn't be possible to fit an rcbo even now, assuming one is available. Otherwise a separate RCD in an enclosure would be alright, sometimes done for showers.
The extension to the lighting circuit may also need RCD protection if the new cables go along walls etc.

An extension to a domestic lighting circuit will always require 30mA RCD additional protection.

 

[Risteard]

I would agree, however it is not what @Zehroni is willing to do, but what the person who is raising the completion or complacence certificate is willing to accept. In my old house still have an adaptable box with two RCD's and two old Wilex fuse boxes supplied from them with MCB's fitted instead of the fuses, one plastic and one plastic and wood base, it would not strictly comply as non of the units are type tested, although since I am not an ordinary person that does not matter, and they are not flame resistance however since fitted in the garage where there is nothing to burn that does not matter.

However I am not doing major electrical work in the house, and so not looking at anything which will require a completion or complacence certificate, with a it is unlikely the work in some way does not need a completion or complacence certificate, likely both, and if one knows the LABC inspector is likely to visit if I was a scheme member electrician I would not want to do anything which he may pick up on, however I do wonder if the LABC inspectors walk around with their eyes closed, as the one inspecting this house allowed the fuse box to be located between ceiling and flat roof with a 9" square hole in ceiling which one could stick ones hand through to just about replace fuses.

So yes a mini consumer unit with a RCBO would do the job, but one is it worth it, and two will an inspector accept it?

Note:- A consumer unit is a type tested distribution unit for use when an ordinary person is in control.

So Screwfix prices a 5 module consumer unit (garage or shower) is £29.99 and a 12 module consumer unit is £31.99 so the cost of parts is nothing really (both unpopulated) where the cost comes in is paying some one so you get a completion or complacence certificate be it the LABC inspector or a scheme member electrician, last time I came to do electrical work needing a completion certificate the LABC charge was over £200 and they wanted me to employ some one else as well to inspect after, after some talking they did in the end agree I could complete the installation certificate, but unless you can show you have the skill it will likely cost around £300 using the LABC route to do latter, and around the same using a scheme member electrician, so may as well fit whole consumer unit rather than a mini one as so little difference in cost now, and it will cost so much to change latter.

The LABC inspection is paid for in bands, depending on cost of work, lowest band is £2000 so that's why so expensive latter. It is not safety or electrical regulations (BS7671) I am thinking about, it is the cost of the paperwork if done latter.

The ordinary person exemption (which no longer is called that) never applies in a domestic dwelling regardless of who lives there. BS7671 is explicit about that.

 

[John D v2.0]

Do I need to replace the whole board or just RCD the newly added breaker for the extension?

So i guess to summarise for the OP, either is fine, but don't forget to RCD the extension to the lighting circuit too.
It may be cheaper to replace the lot assuming the existing circuits don't have faults that would trip in a new CU and would be expensive to resolve.
But you'd want to resolve them anyway so maybe it's a good investment even if more expensive.

 

[SUNRAY]

An extension to a domestic lighting circuit will always require 30mA RCD additional protection.

99% of the time this is correct but even in those rare situations when not 'required' it's a very good idea.

If lights are currently not on RCD there is a possibility of borrowed neutrals.

 

[John D v2.0]

An extension to a domestic lighting circuit will always require 30mA RCD additional protection.

I Forgot about the fact that there would be switch drops for every room!

 

[Risteard]

I Forgot about the fact that there would be switch drops for every room!

Doesn't matter about switch drops. All lighting circuits in domestic (household) premises require 30mA RCD additional protection.