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Adding a loft light with a switch to a ring main

Postby jonmanc15 » Sun Jul 12, 2015 11:39 am

I basically want to add a light and switch in the loft. I want to add it to the main ring.
I have a basic knowledge on electrics I have added wall sockets before.
My plan is to;
Cut into the main circuit just near the hatch where it enters the loft.
Add a 3 way junction box.
Run this 3 core cable into the light.
Half way through the new line I want to add a switch. The switch I have bought has a common, L1 and L2 connection in the back.
Could I make this work if I add the switch mid way through the new line? By cutting the live putting it into Common and back out from L1 or L2.(I presume this wouldn't matter) leaving the neutral and earth uncut?
I hope this make any sense.

Thanks for your time.
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Simply Build It

Postby ericmark » Tue Jul 14, 2015 7:45 am

There are a number of issues not least testing and inspecting however in essence nothing to stop you.

I would use a fused connection unit (FCU) some where with a 3 amp fuse either where you break into ring or a switched one as the light switch.

Some times one can use junction boxes without actually cutting the cable cores this means even if a screw works lose the ring will not be broken. One of the major problems with ring finals is where some work results in two radials being formed instead of a true ring when ever working on a ring it is therefore important to test. If to radials are formed they both will still work but you have wired designed for 20 amp which can have a 32 amp load without auto disconnection which can clearly damage the cable and in extreme cases cause fires.

In the loft there is also the problem if it fails one can end up with a foot through the ceiling.

In my house there is no ring final in the loft. There is only a lighting supply and if it were me I would use a switched FCU near the hatch so you can turn on as you enter and leave. Personally I would use the lighting supply as less likely to trip than a ring final.
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