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Help with Understanding Hall Light Cabling and Swapping Old Light With New

Postby saki » Fri Mar 04, 2016 4:02 pm


I am replacing a hall light with a more modern one. It is operated from a one way switch now but we had extensive electrical work done when we bought the house 17 years ago as we reconfigured some of the rooms. I have a vague recollection that the light might have been two-way at that time. It is a simple old for new job and I noted down how the old light was wired so pretty sure I can proceed safely but I am confused by the cabling.

There are three cables in roof space running to the light. All three reds are joined in a single connector. Two blacks and a blue are also joined in a single connector. There is one yellow cable in a connector. The light was cabled with brown connected to the single yellow connector and blue to the two blacks and blue connector. I have omitted all earths for clarity but they are all connected.

I am assuming the three cables are two of two core and earth and a single three core and earth. I was not expecting to see a three core and earth wire going to the light fitting as I understood that type of cable ran between two switches.

I intend to connect the new light as before ie brown to the yellow connector and blue to the two blacks and one blue connector. But hoping someone can explain why the cables are connected that way and perhaps confirm it is because the light was at one time switched two way?

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Postby ericmark » Fri Mar 04, 2016 10:31 pm

The reds will be permanent line used if you have ceiling fan or emergency lights but not for normal lighting it would seem the red, yellow and blue go to switch, that is unusually normally no neutral at the switch. Often the blue is switched live rather than yellow. Other than three core and earth to switch that is standard wiring.

With two way wiring there is no change at the lamp, the two switches are wired switch to switch and master switch to lamp.
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Postby saki » Sat Mar 05, 2016 1:59 pm

Many thanks for your reply. 2 way switch obviously a red herring. Just non standard use of 3 core cable.
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