Head Scratcher - lighting circuit...

[Aslan]

Hi guys, just after some advice from people older or wiser (or both) than me. I went to wire in a new light in a lounge last night. The light is operated by two switches at each end of the room. When I removed the light cover I couldn't work out what was going on with the wiring. One cable from one of the switches is in normal T&E, but old colours. I am fine with that. The other is 3 core, again old colours but with a solid yellow wire. The yellow wire was connected to the live wires in the light housing. When I tested this it was obviously live.

The problem I have now is that I can get the light to come on, but it is permanently on and won't switch off at all, so I have had to disconnect it. I'm assuming I haven't wired in the switch live properly and have instead wired it as permanently live.

The way I initially wired it was to connect the two lives (red) to the L connection on the light fitting, the same with the neutrals (black) to the N and the 2 identifiable earths to the appropriate earth connection. This still leaves this solid yellow wire doing nothing and the light is permanently live. I don't doubt that i have missed a simple trick with this one but I just can't get my head around it...

 

[monkeyelectric]

Red to red, black to black, blue to bits! Have you got any test gear? When you say a lounge does that mean a customers lounge?

 

[KAS1]

When you say "wire in a new light" do you mean replace a light fitting?

 

[Aslan]

Hiya monkey. yes I have testing equipment. It's my lounge, I am trying to work my way around the house undoing all the offensive work by the previous owner... And there is no end of this. I have basic electrical quals but I only use them to guide my DIY in the house, I'm not professional so haven't come across this before.

 

[KAS1]

There's more to the old sparkying than people think lol

 

[Aslan]

Ah yes, I mean replace a light fitting. As mentioned above I am not a sparky, just an avid DIYer with a basic knowledge. I have my 2391 but no experience, I am just doing up my house.

 

[johnboy6083]

Sorry mate, I can't visualise what you've got. Are you saying that both switches have cables that go straight to the light. Common practice in Domestic I's to take a 2core T&E from the light to the first switch, and then a 3core &Earth from that switch to the second switch.

in the light, one of the cores going to the switch is a perm live and is terminated into the loop, the other is the switch live and terminates into the L(which is where the lamp live is taken from).
at the first switch, those two cores are terminated into L1&L2 (either way round).
the terminations of the 3core are: ensure the cable terminated into the Common is the same both ends, the other 2 cores terminate into L1 &L2.

so there should be 2 cores in L1, 2 in L2 and one in Common.
at the other switch, there should be one in each.
dont forget that the earth should terminate into the back box and if the switch is metal, then link to this from the back box also.

 

[johnboy6083]

Don't forget to test dead, and if needed, identify each core using the continuity setting on your tester. Test each core against earth. This should confirm where each cable goes.

 

[Aslan]

Thanks Johnboy. That makes perfect sense. The confusing element is that the light I am fitting doesn't have loop etc connections. It just has a connector block with L,N,E on it so not sure how to wire this. The switches are wired fine now. One is normal TE and the other has a 3 core coming in, in new colours so I am assuming it has been JB'd somewhere above the lounge previously. I am getting continuity between the solid yellow wire at the light and the grey wire in the 3 core so I am assuming this is the switched live? Sorry for being a nugget, just not quite sure how to crack on with this one, mainly because of the L,N,E connector block on the light fitting really.

 

[Octopus]

Lets hope he's got MCB's or lots of 5A fusewire.

 

[Aslan]

Thanks Murdoch, thats helpful.

 

[Octopus]

Do you have a MFT?

 

[Aslan]

Yes I do.

 

[DJ Ovengloves]

What happens to the continuity when you flip the switch and for the love of God isolate the circuit properly!

 

[Aslan]

Hi DJ. The circuit is totally isolated, and staying that way until I can get my head around it!!! theres no continuity once I flip the switch, which is what made me think that was the switch live? Just not sure how to wire it at the light end, or even if it can be wired in at all as it currently stands...

 

[Octopus]

If the one you took off worked, then the circuit appears to be OK.

 

[Aslan]

Hi Murdoch, yeah I reckon the circuit is fine. I guess the key question is how to wire 3 core plus earth and TE into a light fitting with a connector block on the light fitting for only L,N,E, rather than live, loop etc?

 

[Octopus]

How was it wired before you took it apart?

 

[Aslan]

The live from the old light fitting was connected to the solid yellow wire. The lives were connected together in a connector block and the neutrals and earths were connected to the old light fitting. Just seems really odd and can't get my head around it...

 

[Octopus]

So why don't you simply connect the new one as the old one was connected?? I think I know what's going on!