3 gang 2 way dimmer switch - help!

[AnonymousImport]

My kitchen has 3 sets of lights.

2 sets are of 4 spotlights on a 2 way switching system. The last set are an independent set of under cupboard lights.

I am trying to replace the 3 gang switch with a 3 gang dimmer.

The dimmer has 3 sets of terminals, each marked L1, L2 & C.

I have 3 sets of 4 core wiring inside the box - red (L1), blue + red sleeve (L2), yellow (C) & earth (to metal box).

I have wired each 4 core as above.

2 sets of lights work, one doesn't, it has no power to any of red, blue/red or yellow.

When I dismantled the original box I marked all the wires per set of lights.

I didn't notice until too late that there was a red wire bridging 2 terminals.

Is something being shared?

Where should the bridge wire go?

I have tested all three dimmers and am happy they work.

Any advice would be very appreciated having spent all day Sunday trying to get this to work. Thanks.

 

[amtodd]

You don't say which set of lights does not work.

If it is one set of the ceiling lights, may well be a shared earth, but if so, where does the other end terminate?

If the under cupboard lights are faulty, perhaps they were an after thought, and in order to avoid chasing the wall out again, the Live for some circuits was shared, leaving a cable free to run a Neutral down.

You'll need to have a look at both sets of switches for the two way, and all three sets of lights to see what is going on. Turn the power off, remove the lamps and trace what each wire is connected to.

 

[SimonMP]

Thanks Amtodd, can you help some more?

It is the second set of ceiling lights that aren't working.

I am tempted to use the bridge wire to share the common from the under cupboard lights. The u/c lights are not on a 2 way switch.

This would bring power to the common and allow switching between L1 & L2.

Any thoughts?

 

[amtodd]

Oops, realised I typed in "shared Earth" but meant "shared Live". Sorry.
More than happy to help, however I'll need a little more info. If you can trace all 12 wires through to their other ends, and through to either fittings, junction boxes or roses that would assist. I'll then try and work out what you have and compare it to what you should have!

My concerns are:
1)if you need to take power from another circuit, you have a "spare" wire and you will need to make sure it is earthed - preferably at both ends - which is fine if it is not connected to anything, but may give you problems if it is really a Neutral;
2) if you take a Live feed from another circuit, is the Live on the same trip / fuse circuit as the Neutral? May give you grief if they are not, especially if the under cupboard lights are RCD protected and the lights are not.

 

[SimonMP]

Shared live makes sense.

1) The circuit borrowing power is earthed to the recessed metal box.

2) All three circuits (2xceiling, 1xcupboard) are on the same trip switch.

The ceiling circuit that isn't working is wired exactly as the one that is working.

The only difference is that there is no power at the common on the circuit that isn't working.

My house is 4 yrs old and wires are all behind plasterboard and chipboard tongue & groove flooring. Tracing them would be v. difficult.

My guess is that ceiling1 is wired the same way as ceiling2 but needs to borrow power from Common1.

I hope that makes sense,

Cheers, SMP.

 

[amtodd]

Sorry Simon, I'm not explaining myself very well.
You don't need to physically follow the wires to their respective ends - if you use a continuity tester you can determine where they come from. You will need to turn the power off and remove the lamps and then test.

The 3core +E cable you have for the non-working circuit has to be connected somewhere. I'm guessing from what you have explained so far, that this will be connected to the other switch and not to the fitting. Check with a tester. Where ever it comes out, there will be a spare unused core somewhere.
If you must leave a cable in a building that has no purpose you should ensure it cannot be connected by accident. A common approach with unused cores is to cut them back so they don't touch anything. My preference is to crimp all cores in an unused cable together at both ends and to earth all uused cores - accidental connection of either end will blow trips or fuses instantly the power is reconnected, a pain but safe.

Hope this helps. Still struggling with it, email me ([email protected]) - I'll give you my number and try to talk you through it.

 

[YetAnotherAnon]

simon, have followed the discussion on this problem, and builder amtodd may not be, but cautious he is, and I agree to an extent. It indeed sounds like you have two two way circuits but one is missing a live. sharing the live may solve your initial problem, but without tracing out the core you will have left over you cannot be certain it will not become connected to something (live or neutral) in the future either by additional works or change of direction of switches timeclock or cable movement. Trace it through, and if it comes from a rose or J-box, reconnect it to live and you have solved your own problem. If it turns up at the other switch (most likely), connect it to earth at both ends. If you can't find it, connect the end you have got to earth, as amtodd said.

That's the nice version. The time served sparks version follows.

The wiring regs say a competent person has to do electrical wiring. This does not require a professional or exams. but it does require understanding of what you are doing. Failing to take basic steps to make the job safe is not a sign of competence. Electricity can dangerous, and bad wiring causes more fires than electrocutions. With no firemen about at the moment, if you can't be bothered to get hold of a meter or continuity tester and trace the spare core to make the job is safe, get in someone who will.

 

[SimonMP]

Just to close this....

Thanks to all for advice.

I have fixed it this weekend. I opened up the other switch and traced the wiring.

Everything is fully earthed. The sharing of the live became more apparent once I had access to the other end of the circuit and traced the wires.

My only advice on this is....

Before disconnecting a working 2 way switch system, fully document what wires are connected to which terminals.

This seems obvious but with lower light levels, once the power is cut, it is all to easy to be over confident about which wires go where and miss this step. It would have saved a lot of wasted time.

Thanks to AMTodd & Sparks,

SMP.