Converting Loft

[Duzzer]

I'm converting my loft and need a question answering about electrics. I fitted
a combi a few years back( I'm a Gas Eng) and took cylinder out. The fuse spur for the immersion heater is still in the airing cupboard. Question is can I extend the cable into loft and use it for the lighting and sockets for the loft so there on their own circuit? Also i'm only gonna use about 4/6 sockets would a radial circuit be ok or should I still fit it as a ring main?

 

[Steve]

What will you be doing up there? What sort of electrical equipment?

Your idea sounds fine though. A radial will be fine for most purposes. Fit it in 4mm if you can - then you can have a 32 amp MCB. Use a 3 amp FCU for lights (dont have them on the upstairs light circuit)

This is all notifiable though.

 

[Duzzer]

No en suite just a bedroom, will have radiators so no heavy elec stuff like heater's.

 

[333rocky333]

You need to know the size of the cable at the spur,
and where it comes from.
Find the fuse for the spur ,see what size the fuse is and whether any thing else goes off with it turned off.

You cannot extend off that spur in 4mm and use a 32a mcb UNLESS that spur is ALREADY 4mm which is unlikely

If it is 2.5mm and you know 100% it is direct from the fusebox
You still could extend it as a radial

You MAY be able to extend it with the same size 2.5mm cable to an unlimited amount of sockets subject to the area being no more than 50 square meters,

Also subject to total cable length / volt drop /Earth loop impedance calculations and instalation methods,etc. (20 metres as a rough guide)

The maximum fuse/mcb MUST not exceed 20 amp

You would also need a FCU (spur) in the line somewhere to fuse the lights at 5amp you would then wire the lights from the output of that in 1.5 to the light, and in 1.5 from the light to the switch,if you want to do the connections at the light.
Or you can use that Fcu as the switch and just wire the output direct to the light only.


To form a ring circuit extended from that spur would not be advised though

 

[Duzzer]

I've checked the fuse at the board and it's on 15amp it's on it's own. So if it 4mm or bigger that's fine to use i'm getting an electrician to do it just would have needed him earlier in the project to run fresh cable from meter.

 

[ban-all-sheds]

He can't (well, he can, but there's no point) do the addition in 4mm² because he wants to extend the old immersion circuit into the loft, and that's unlikely to have been done in 4mm²....

So assuming 2.5mm², that can be extended into the loft as a 16/20A radial (MCB rating depends on a number of things, and used for sockets and, via an FCU, lights. The existing FCU in the airing cupboard can be removed.

Whether 16/20A will be enough depends, as you say, on what he's doing up there, but unless it's some kind of clandestine horticulture it probably will be.

As for notification, unless there's going to be a bath/shower room up there then it isn't notifiable - it comes under item 2c in Schedule 2B.

There remains the thorny issue of testing what would be a significant addition to the circuit. The best plan would be, paradoxically, to notify it, i.e. add it into the notification for the loft conversion - that way it'll get inspected and tested by LABC.

Duzzer - can you estimate how long the complete circuit would be, all the way from the CU, and would the cable run in insulation anywhere?

 

[Duzzer]

The run from CU to end of sockets would be about 20m, say GF 3m 1st floor 3m then plus 4m along then 10m around loft say about 10m insulated.

 

[Duzzer]

Supply to immersion was only 2.5 so electrician is running totally new supply from meter. Cheers for all your help.