Double-switching problems

[GB]

I asked a builder to replace a plaster-board wall, and to do that he disconnected the light switch. When he reconnected it, he seems to have connected it up wrong. It was one of those switches for a hall light, so that you can switch it on/off at two locations.

It ought to be simple enough to sort out, but the builder got into a panic and seems to have reconnected all the wires at random, including opening the ceiling rose and possibly fiddling with the wires there.

Of course, all the wires are buried in the walls/ceiling and none of them are colour coded correctly any more. I think the original wiring may have been done quite a long time ago.

I feel I ought to be able to sort this out myself, as I have a degree in Physics.

Is there a normal layout for these switches, as it seems to me there could be more than one way of wiring it to achieve the desired effect?

Is there a trouble-shooting guide?

I suppose I could start off by producing a chart of what happens when the lights are switched on/off. In a nutshell, the light can be switched on at either switch, but then it has to be switched off again at the same switch.

The builder put a new switch on the new wall. I have checked that it has a common and two other contacts marked L1 and L2. This looks like the right sort of switch to me.

Anyway, any help would be appreciated.

Thanks

Geoff

[Dave Plowman (News)]

This might help. Check the wiring on the other switch for colours. Swapping L1&2 doesn't matter.

L1 L1 0===========0 0===========0============= Line | \ / | C 0================================O C \ / \ / 0===========0 0===========0============= Switch return L2 Optional L2 Intermediate

[john2]

That a very complicated diagram, even for a physicist. This is a bit simpler, taking out all redundant lines:

L1 L1 0===========0 | | Live ========0 0 ====================== Lamp =========Neutral \ / 0==========0 L2 L2 switch1 switch2

john2

[Andy Wade]

There are two standard methods for wiring two-way switching. If your wiring is reasonably modern, in flat twin-and-earth (and triple-and-earth) cable, this reduces to one standard method. Dave Plowman will be along shortly to post his usual diagram.

Look at the other 2-way switch and ensure the the colours of the 3+E (red, yellow, blue) cable are connected the same way at both switches.

One of the switches will have a second cable, this time only 2+E (red & black, and the black should sport a red sleeve). Here the two wires connect across the L1 and L2 terminals (either way round). Neither should connect to the COMmon terminal.

All earths should have green/yellow sleeving and be connected to the earth terminals in the back box (also to any earth terminal on the switch itself, e.g. for a switch with a decorative metal front plate.

[Andy Wade]

Yes, but that's the *other* standard method, only used if you're wiring using singles in conduit. Dave's diagram is far more likely to be what the OP actually needs.

[Christian McArdle]

There are indeed a number of ways of wiring these things. However, the best and most common method was shown by Dave Plowman. John2 produced a different method which has significant disadvantages, but is still regularly found, especially in older installations.

It may help us to indentify which method if you explain what cables are present at each point. Ignore any earth conductors. Only count proper coloured and insulated conductors. Please tell us how many 2 or 3 conductor cables are at each switch and the ceiling rose.

Christian.

[Dave Plowman (News)]

Your way involves jointing a cable somewhere in most installations. Mine doesn't.

[GB]

Thanks all for the help. I'm not currently staying at the house, so I will need to go over to check it out. I'll report back later.

[john2]

I was trying to draw a basic circuit diagram to get the point across, rather than a physical wiring diagram which is a lot more complicated. Ah well....

john2

[Dave Plowman (News)]

Most recent wiring uses the switch pair from a ceiling rose method, so that both these wires arrive at the one switch on a two way circuit. Your diagram suggests you need to joint one wire to feed the two way circuit between the switches if this is the case. If someone doesn't understand how a two way circuit works this only really adds confusion as they're likely to do just that.

[GB]

I have now checked the wiring at both switches and the ceiling rose

Ceiling rose:

Two black wires come in, one with a red sleeve - connected to opposite poles of the bulb holder.

Also, two red wires come in, connected together in a spare terminal, not connected to anything else.

Switch 1:

Red to common Blue to L1 Black to L2

Switch 2:

2 red wires connected to common Black to L1 Different black wire+ blue wire connected to L2

I am afraid that without testing it all out with a continuity tester, I am not at all clear what is connected to what.

[Dave Plowman (News)]

You can't blow a fuse by experimenting, so I'd try moving one of the red wires in SW2 to LI. If that doesn't work, try moving the other one.