Second Consumer Unit For Annexe.

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tomvassie

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Hello Everyone,

I'm after a little advice if possible please.

We are in the middle of building an extension on the annexe of our house, the annexe currently has one ring main and one lighting circuit coming from the main house CU.

The main CU has one RCD(100ma) protecting all ring mains for both the annexe and the main house, all lighting circuits and not on RCD.

The current annexe kitchen will be moving, however there is no cooker feeds to worry about as they are gas, the old kitchen will become a utility room.

My intention is to put a new CU in the annexe fed from the main CU and for it to have the following layout.

RCD1 (30ma)

1)32a - existing ring main (removed from old CU)

2)32a - small ring main for new kitchen (4 double sockets with a couple of switched fused Spurs for under worktop sockets for appliances)

3)32a - ring main for all other rooms in the new part of the annexe extension.

RCD2 (30ma)

4)16a - immersion heater

5)6a - existing lighting

6)6a - new lighting

So my question I need to ask is regarding the cable between the two CU's.

The distance between the two is around 25m max.

My plan is to use 16mm 3 core SWA protected by a 45 or 50a mcb on the non RCD side of the old CU.

Am I going about this the correct way?

And a second question,

In the new annexe kitchen (currently a lounge/front room) there is a couple of sockets on the existing ring main. They are on the opposite wall to which the kitchen units will be fitted, aprox 4m wide room.

Would it be incorrect to have the new kitchen sockets on their new ring and the existing sockets on a different ring in the same room?

Sorry for this being a bit long winded, but I've tried to cover everything, please ask if I've missed anything.

Thanks in advance

Tom.

 
Hi Murdoch,

Could you expand a little? Complying to regs for the electrical side or the building side?

 
electrical work such as you are planning to do will come under building regulation compliance.

ie, it is not simply a matter of wiring it up,

you will need approval from building control to do this type of work, planning permission basically,

or, an electricain registered with a scheme that has permission to approve this for you, to put it very simply.

 
Hi Steptoe,

Thanks for your reply.

The extension has its planning permissions and building regs, but as far as the electrical side goes, I have been lead to believe that the work would need to be approved by a registered electrician to get the sign off from building control?

I could be wrong here?

 
yes, or you could have had it included in your planning application.

the way you are planning to configure your consumer unit would NOT comply even half heartedly with the current version of the wiring regulations  BS7671, your electrician should be able to advise you better of how to do this.

you will NOT be able to get the work approved by a registered electrician,

it has to be carried out by a registered electrician,

NO proper electrician, registered or otherwise, would ever sign off someone elses work.

 
Steps - that's not true though, is it?

The OP can legally do the work as long as it is notified to building control (either as a separate entity or as part of a planning application) and pay them a fee to have the work tested and certified. They may want to inspect at certain points.

So you can legally do electrical work in your own home and get a 3rd party to certify it. Just not drag any old electrician in off the street to certify.

In terms of what the OP suggests - what is not compliant with current regs?

 
Apache,

the first line of my previous post,

not compliant would be adequate seperation of circuits to minimise nuisance in case of a fault,

electrical work such as you are planning to do will come under building regulation compliance.

ie, it is not simply a matter of wiring it up,

you will need approval from building control to do this type of work, planning permission basically,

or, an electricain registered with a scheme that has permission to approve this for you, to put it very simply.
this

yes, or you could have had it included in your planning application.

the way you are planning to configure your consumer unit would NOT comply even half heartedly with the current version of the wiring regulations  BS7671, your electrician should be able to advise you better of how to do this.

you will NOT be able to get the work approved by a registered electrician,

it has to be carried out by a registered electrician,

NO proper electrician, registered or otherwise, would ever sign off someone elses work.
and this

 
Hi Apache,

This is kind of what I had in mind, paying for the completed job to be inspected by building control (or who they appoint to do it).

Also yes I'm sure that my layout of the new CU could do with some swapping about. And also I forgot to add to the list about fire detection which I beleive will need to be added to comply with regs.

 
Steptoe,

Great, thanks for that advice. I will get on to that tomorrow, I have got the building inspector in tomorrow or Friday anyway so will talk it through with him.

Nothing electrical has been started yet anyway. But I'm just trying to make plans for when I do, and start getting some materials together.

I didn't really want to buy 25m of 16mm Swa only to find out I could of used 10mm or should have got 25mm!

 
off the top of my head, 16mm 3c SWA should be ok, if you are terminating into a plastic enclosure you will need special earthing nuts for the glands,

but, it will depend a lot on your incoming Ze, or Zs at your point of connection , that is, the earth loop impedance reading at your present CU, as to if 16mm cable will be sufficiently big enough.

if you have a TNS supply with a high-ish permitted reading on Ze then you may very well struggle to get 16mm to comply with permitted Zs/Zdb levels, and volt drop on final circuits.

 
I am fairly sure we are on a TNS supply.

I'll get this all checked out and get things squared up with building control before I go any further.

Thanks for the advice guys.

 
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