Wire to the consumer unit

paulb4 · 4 Jul 2010

Hi all,

on my consumer unit I appear to have some spear mcb's. I plan to wire sockets in the shed.

I have power to my shed via a extension lead.
is it as simple as cutting of the plug and wiring to the mcb or can I not use that wire?

1john · 4 Jul 2010

NO! dont use that cable, you more than likely need steel wire armoured cable, also you need to be aware of part P too.

paulb4 · 4 Jul 2010

The cable is going straight through to a brick shed that has no damp but I will use armoured cable if that is whats right.

Once I wire up to the circuit breaker, do i then wire to another circuit breaker for power?

Unfortunately I am not in a position to afford a electrician for such a small job but I willing research as much as I can before doing this.

1john · 4 Jul 2010

Ok well a full discription of the work, property layout, cable type and size, mcb type and size, RCD rating (f any) will be a good starting point. Are you aware of Part P ??

paulb4 · 4 Jul 2010

The shed is right next door to the consumer unit just a brick wall in between.

I want to put direct power in the shed, just sockets.

There is no RCD on the consumer unit.

I have never done this before I only have a basic knowledge of electrics. I do not have a part P.

To answer your questions I will post a photograph tomorrow if you can come back then. Thanks for the help.

1john · 4 Jul 2010

Part P is not something you have, it is a building regulation that needs to be complied with, you need to inform your local authority building control of the work BEFORE you start or employ someone to complete the work and self certify that the work complies.

paulb4 · 4 Jul 2010

I am here primarily to get help and advice on how to wire sockets in my shed.

I will not be starting this project yet but when I do I will make sure all that is looked into.

I will post a picture tomorrow with some questions.
thanks.

TonyW2 · 5 Jul 2010

paulb4 said:
The cable is going straight through to a brick shed that has no damp but I will use armoured cable if that is whats right.
Unfortunately I am not in a position to afford a electrician for such a small job but I willing research as much as I can before doing this.

Pity you can't turn the clock back

Before recent regs, you could have wired from a spare MCB straight through the wall (preferably with a sleeve) to a double socket. This would have created a simple spur into an adjacent room. Adding a FCB in the shed on the way would have been nice.
Now, you have a new external socket and the supply needs to be on a RCB, with protected cable etc.

I am NOT qualified to advise. No doubt somebody with more sense than this average DIY er will advise.

Chri5 · 5 Jul 2010

For your job you need to consider what you intend to run in the shed.

Say it's a freezer, light and a double socket for the odd DIY job. If that's it then a 20 amp MCB with a 2.5mm TE cable would be okay.

As everyone has mentioned new circuits are notifiable work. Part of the reasoning is that new work should be to current standard which includes an RCD or RCBO on the circuit.

If you really must DIY then you should comply, so hows about:-

2.5mm TE cable
20 amp mcb at existing CU
New sub board in shed with RCD
20 amp mcb for sockets in shed
6 amp mcb for lights

As for the total potential load being 26 amp back to the main CU that would be handled by the 20 amp mcb,

If you need more power in the shed then a 4mm TE will take 30 amps.

Now all you need to do is confirm your earthing arrangements, bonding for water and gas, read up on testing, get some test equipment, and then you will have a 95% safe job, which is 100% not notified and would be questioned if there's an insurance issue or house sold.

Apparently you can only be prosecuted by the Council for failure to notify for a 6 month window from finish of work.

ccam108 · 7 Jul 2010

Would a garage CU really be needed? How about a 20A radial on 2.5mm T&E (assuming it doesn't need de-rating) with as many sockets as needed and a 3A FCU for a light?

Colin C

ColJack · 7 Jul 2010

TonyW2 said:
Now, you have a new external socket and the supply needs to be on a RCB, with protected cable etc.

no you don't have an external socket.. the work inside the shed doesn't need notifying at all unless it's a new circuit to the CU..

he can still do this non-notifiably ( is that even a word? )..

the new socket can connect to an existing circuit in the CU ( such as the downstairs sockets ) and it's then a spur from the sockets.. ( you can spur form any point, including the OCPD ).
since this is not work outside ( it goes straight through the wall to the shed, no external connections ) then it's not notifiable.

this of course limits you to one double socket if your sockets are on a ring and protected by a 32A breaker.. if however your sockets are on a radial with 4mm cable and a 32A breaker, or 2.5mm cable and a 20A breaker then there's no real limit to how many sockets or fcu's you could add ( light ) as it would then just be a branch off the radial.. ( more reason to install radials.. )

davelx · 8 Jul 2010

ColJack said:
this of course limits you to one double socket if your sockets are on a ring and protected by a 32A breaker..

Not if he puts an fcu in - then he can have as many sockets as he likes, subject to a max overall load of 13A, of course. That may be all he needs.

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Wire to the consumer unit

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