Different lighting circuits at a double switch

[Ron Lowe]

Hi all.

At my house, we have some outside floodlights ( 3*500 w halogen ) which were obviously retro-fitted by the previous owner.

These have been added to an existing lighting circuit with the obvious result that the breaker must have been tripping.

I was looking at the CU today, and I see that the other lighting ccts are

5A, but this one has had a 20A breaker installed!

I intend to correct this now I've noticed!

There's a spare way on the CU I can use for a dedicated circuit, that's no problem. However, the switch for the floodlights is a double switch, with one switch operating some internal lights ( and 2-way at that ), the other operating the rogue floodlights.

Is it permitted to have a dual light switch fed from seperate circuits? It might lead to someone incorrectly assuming that the switch was isolated when only 1 cct was isolated, was my concern.

[Owain]

It's very common on stair/landing light switches.

Yes it might, but (a) they should test all the wires for live before playing with the wires, and (b) if you put a little warning notice inside the switch box that will serve as a useful reminder to you and caution to anyone else.

Owain

[Andrew Gabriel]

Yes. It's quite common with the landing light switch which is often combined with a downstairs light on a different circuit. You must keep the two circuits electrically separate (no sharing of neutrals, etc, although cross-connecting earths is OK).

It might, but people shouldn't be making any such assumption.

The floodlamps could go on a 10A circuit. However, you might want to consider fitting lower power bulbs -- 500W is usually way OTT outside at night in a domestic situation. If they are left on for any time, find some energy saving IR-reflecting coated bulbs. The GE ones are rated 375W (500W equiv) and 225W (300W equiv). B&Q have them sometimes, but not always.

[Dave Plowman (News)]

Yes. Upstairs and downstairs hall lights is the common one.

Never, ever, *ever* assume something like that is isolated. Test always.

[Bill]

In message , "Dave Plowman (News)" writes

A bit like the light switch in a friend of mines lounge that I looked at today. The complaint was that the lights in the conservatory, which her son uses as a bedroom, were not working. The switch which is in the lounge, part of the original house, did not have any power to it, the bulb in one of the lights was physically broken and shorted out. I removed the bulb and went to find why there was no power. Trips all OK, checked before hand and none had tripped out. Eventually found a fused spur on the upstairs power ring with a blown 3A fuse that fed the conservatory lights. Replaced it and all was well. The slightly worrying thing was that although this is apparently a common practice the light switch appeared part of the lounge and did not look like an addition although it must have been. My thought is some one turning off the downstairs lighting circuit and then working on the conservatory lights could have a rude awakening.

As Dave said "never assume" "Test always"

[crb]

You must keep the two circuits electrically separate

Is there a specific technical reason/regulation for this (apart from that vague term "Good Practice")? I would have thought that if the cable IR drop and maximum current criteria were met, then there would be no reason against doing so.

CRB

[Dave Plowman (News)]

The obvious one is RCD protected circuits. Apart from the very real safety issues when doing maintenance.