Changing a light switch

[Graeme]

Simple enough job, usually.

We have a pair of 2ft florescent tubes under kitchen wall cupboards, daisy chained and controlled by a switch within one of the cupboards. The switch is standard wall mounting, with back box. The switch started to play up, not always supplying power, so yesterday, I replaced it.

The incoming power is standard grey sheathed T&E, and I rather suspect comes as a spur from a nearby 13 amp socket. Live and return are red and black. Power from switch to lights is ordinary flex, as you would use with a table lamp, or similar, with modern colours - blue, brown etc. The switch itself was a monstrous thing, obviously designed for far more than a light. Possibly a cooker. Twin pole, plus substantial earth connections.

The new switch I installed is an ordinary wall light switch, single pole, so I wired the two lives to that, and directly connected the two returns and two earths using a chocolate block, tucked in the back box behind the switch. Switch itself is plastic, as is the back box. Have I done anything slightly naughty, inadvisable or dangerous?

[Brian Reay]

Doesn't sound good.

The 'spur' is worrying if nothing else. The ring main will be 'fused' at

30A, you've got lighting flex protected by the same 'fuse' (or breaker) by the sounds of things.

[Andy Burns]

What size is the T&E cable? can you trace it to where it comes from?

If it's a spur from a ring circuit, but isn't a *fused* spur, you likely have a 32 amp MCB (or 30A fuse if older) protecting the thin flex to the lights ... if it's actually a re-purposed cooker point instead of a spur from the ring, it could be worse on a 40A or higher MCB.

[Graeme]

Hmm. Yes, I had not thought about that. I was thinking only of my switch substitution. I'll have to do some experimenting, and see which fuse controls those lights. I changed the switch live.

[Chris J Dixon]

Yet you still need to ask:

Chris

[Muddymike]

That doesn't sound as if you have done anything dodgy. But the original installer...

Mike

[Bill Wright]

You could change the switch for a switched fused spur unit and put a 2A fuse in it.

Bill

[Graeme]

In message , Bill Wright writes

That sounds like a perfect solution. Thanks.

[Graeme]

Well, yes, although I was really referring to the wiring, rather than how I achieved it. Having said that, I was very careful, firstly disconnecting the returns, one at a time, and joining via a chocolate block, then same for the two earths.

Next, I removed the unpowered live return, and connected that to the new switch, then finally the live feed, having used a meter to establish that the switch was off. I used well insulated screwdriver and needle nose pliers, carefully and slowly.

[Jeff Layman]

But you no doubt assumed the wiring was correct in the first place. There's no guarantee of that, particularly as an obviously unsuitable switch had been used in the first place, and you suspected connection from a 13 amp spur. Why didn't you switch off or pull the fuse at the box before working on it?

Just out of interest, did you know there if was a consumer unit with a working rcd/elcb before you did any live work?

[Graeme]

In message , Jeff Layman writes

I checked that the red was indeed live before starting.

Fuses only here.

[John Rumm]

Nope, what you have done is fine...

What was done before you got to it might be a problem - but that is not your fault. If the source of the supply is a socket circuit, then it should come from a fused connection unit somewhere. Otherwise the flex to the lamps is unlikely to have adequate fault protection.

(note this is not huge danger since the chances of the flex getting damaged in that installation scanrio is presumably vanishingly small, and there are not many likely failure modes of the lamps that will result in a hard short circuit)

[John Rumm]

Only thing to check is that the T&E coming into it is of adequate size.

Chances are it is, however if you found for example that the circuit was protected by a 30A BS3036 rewireable fuse, and the extension had been done in 1mm^2 T&E, then that bit of T&E may not have fault protection without the fuse at its origin rather than its end[1].

(still a tiny risk in absolute terms - it probably falls into the category of stuff I would not do in the first place, but would only bother fixing if there were other reasons to change stuff)

[1] i.e. this is a variation of the situation that can leave a spur unprotected on installs with old 2.5mm^2 T&E that only had a 1mm^2 CPC. (modern 2.5mm^2 T&E has a 1.5mm^2 earth)

[Brian Gaff]

Well, it all depends on whether the wires can be trusted on their sources I'd say, assuming this, I think I'd feel happier if a fused spur was there rather than a light switch with, say a 3 amp fuse in it. Brian

[DerbyBorn]

Bill Wright wrote in news:ob05u9$1lhp$1 @gioia.aioe.org:

+++++1

[Graeme]

Thanks John. I'm no electrician (!) but it was the physical size of the incoming T&E that first made me suspect it to be a spur from the power rather than lighting ring main. It is what I would associate with a power circuit rather than a lighting circuit.

Someone mentioned an ex cooker socket. No, not that heavy, and I know exactly where the ex cooker cable terminates, even though it is no longer in use.

[Graeme]

In message , John Rumm writes

My thoughts exactly. The flex supplying the lamps is there to inspect, and easily seen, so I am confident that any damage would be noticed.

[John Rumm]

As suggested earlier - if you have a large enough T&E coming in (which by the sounds of it you do), then a switched FCU used as a switch will do the job nicely.

[Scott]

One man - one vote :-)

[DerbyBorn]

Got a bit excited that the right answer eventually came!