Wiring Problem After 2 Gang 2 Way Switch Like for Like Swap


Postby clueless_idiot » Sat Oct 01, 2016 6:33 pm

Switch1.JPG
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Hi, earlier I tried to replace a 2 gang, 2 way light switch in a like for like swap. A simple enough task you would think...

As I was working I took several photos to try and remember the wiring set up so I could copy it but stupidly didn't photograph the connectors when I took the duct tape off. I then unscrewed them so I could force out the wedged in, knock out box. When it came to later wiring up the new switch I couldn't figure out what went there.

As you can see the wiring is pretty old school. From what I've read the red wires are live, the blue and yellow wires are switch lines (never seen these before). Could someone please explain how I can now wire in the new switch plate? Thanks.
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Switch2.JPG
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Postby kbrownie » Sun Oct 02, 2016 8:31 pm

Firstly it looks like backboxes have been replaced?
The sheath of the cable should enter the backbox, which by the pictures it does not! Also the knock-out holes should be grommeted to prevent the cable becoming damaged, by rubbing on sharp edges.

Have pictured both switch points, as they look different.
If so did not consider noting down the cables and terminals on both occasions?

There are a number of ways in which switches can be wired and there are also a number ways that two way switch can be done.

Do you have a means of testing the cables for continuity and voltage, as you have disconnected them now, without identifying there function, testing will be required.

On the set up you have, it looks like you have one where a single red will be supplying a live to the com/L of the one switch, there maybe only one live cable coming into the switch, so for two gangs a link cable across each gangs (com) would be required.
Then I would expect the other reds and blacks to be the switch lines so red in L1 and black in L2

At the second switch, the red that would be expected to be live actually goes directly to the light. So on switch will have common/permanent live and the second switch will have the spare reds going to the lights.

The second switch shows a different combination of core colours, so we need to know if anything else is connected to this conductors?
That is why you need to do continuity tests and then voltage test, using suitable and safe electrical test equipment, Please do not use a neon test screwdriver, they are unreliable and dangerous, a two pole instrument must be used.
The pictures are too clear so a close up of all conductors and a little more info of numbers. colours and if they are paired up in sheaths.
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Postby clueless_idiot » Mon Oct 03, 2016 5:35 pm

Hi, after reading your reply I got a qualified spark to come up and test the wires. He found there was no earth wire connected to the switch from either cable so it's been a real cowboy job by whoever wired it up originally and will take a bit of rectifying now.

Thanks for taking the time to post a reply to my question.
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Postby kbrownie » Tue Oct 04, 2016 6:48 am

Not necessarily a cowboy installation, it has not always been a requirement to supply and earth to a lighting circuit (so that would depend on the date of installation?).

It could be possible that the earth (CPCs have been snipped back and still exist in the sheath and sometimes it can be rectified by joining/adding an extension to it.
But as the sheaths do not enter the ungrommetted entry holes, that may now be not the best way forward.

You are allowed to but class II fittings on unearthed lighting circuits, but you cannot use class I fittings.
https://en.wikipedia.org/wiki/Appliance_classes
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