DIY Doctor

Adding Smoke Alarms to Lighting Junction Box

Postby keepalex » Tue Mar 19, 2019 9:50 pm

Hi Everyone

I'm a first time poster and completely amateur diy-er. A draft of this post got lost so I hope this isn't double posted.

I am intending to add smoke alarms to my upstairs lighting circuit. There is an old junction box with permanent live under the floorboards, which I am planning to carpet over. Picture here.

From reading here and elsewhere I understand that nowadays a junction box like this needs to be accessible, but it would be tricky to move this to a new location. The current box also doesn't have much room for the new cable.

I'm therefore hoping I can replace the box with a maintenance-free junction box. If that's correct, could please someone recommend a box that I could use?

Many thanks for any suggestions or advice.

Alex
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Postby ericmark » Wed Mar 20, 2019 2:02 pm

There are loads of boxes, but first question is what to do about the pre-1966 wiring with no earths connected.

Although there is no requirement to upgrade existing, any new bits must have an earth even if the fitting is class II the earth must be available.

I tried to connect earths once when working in the Falklands where some one had not connected them, it was a nightmare. There was it seemed a junction box in the roof space and I could not assess it.

You will need some test equipment, normal took is a loop impedance meter however rather expensive. There are lighting junction boxes designed in the main to replace ceiling roses which normally double as junction boxes, however if I as an electrician was asked to sort that out, it would have to be day rate, or sucking of air through teeth and quote for rewire.

Wiring like that is not permitted today, and any electrician would need to raise a minor works certificate to cover the work, so because of cable length likely that one box would be replaced with 4 or 5 but main problem is not under floor boards where one can gain some length, but at switches where cable is plastered into the wall, and main feed again likely plastered into the wall.

Personally I would replace cover and use battery smoke alarms. It could take longer to sort out than it would take for complete rewire of lighting circuits. Also likely you will also need a new consumer unit, as likely no RCD protection in old one.

I would get a quote for a rewire, then don't touch electrics until you have the money, as likely one thing will lead to another.

Sorry to be bringer of bad news, in 1966 the rules changed and all lights needed an earth, then from 2008 we have had a string of changes mainly to do with RCD protection and wires not being able to fall on fire fighters. You don't have to upgrade unless you want to rent out the house, but it means to add anything costs a lot of money as anything new does need to conform with BS7671:2018.
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Postby keepalex » Wed Mar 20, 2019 5:54 pm

Thanks so much for your concern and good advice.

It's hard to tell, but there are in fact earth wires on all these cables - but they're wrapped around the back of the junction box. With the exception of the very old cable in the picture (which was to the doorbell and I've already replaced) I'm sure they're all much newer than the 60's.
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Postby ericmark » Thu Mar 21, 2019 1:58 am

Glad to here it. I would consider a central heating wiring centre to have the terminals required and cable clamps.

I know junction boxes should be accessible however know one seems to declare what is regarded as accessible and you normally only test every 10 years.
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