Yellow wire with 75 volts?


Postby JohnnyC » Mon Apr 13, 2009 10:44 am

I have one 3 gang switch in the kitchen and have been replacing a light for some spots, so have been adding wiring for the spots. There are 4 cables coming together where the light was fitted and I have replaced some plastic connectors with a 20 amp connection box to tidy things up. I thought I had reconnected everything exactly as before but must have made an error as the spots are permanently on so I can't have connected the spots to the switch correctly. One of the cables is 4 core, earth, red, blue, yellow and when the switch is flicked on the yellow becomes live which seems to suggest this is the switch live feed and my spots should be connected to this and neutral back to neutral in the connection box. Only thing is that when the switch is off the yellow has 75 volts coming through it. How is this possible? Have I wired up incorrectly or is the switch faulty or is it something else?
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Postby kbrownie » Mon Apr 13, 2009 7:08 pm

How do you know there is 75volts in the yellow conductor, what instrument are using and have you made good contact?
You say 4 cables from ceiling one with four cores, so what else is attached to cables at ceiling rose is there a fan?
You also said you have removed connection blocks and replaced by junction box what access have you left to this accessory, you can't leave these up in a ceiling void without easy access for later inspection.
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Postby JohnnyC » Tue Apr 14, 2009 6:28 pm

I have a voltmeter and have made good contact and the meter reads ok when used on other wires. There isn't a fan
The other cables are :
one is the live lighting circuit (red,black, earth)
one is the four core cable and is from the switch (red, blue, yellow, earth); the blue from this feeds the red in the third cable which powers one of the lights in the kitchen (red, black, earth)
the fourth cable runs on to the dining room to complete the lighting circuit there (red, black, earth).
Apart from the blue to red noted above all reds are connected to red, blacks to black and earths to earth and I have now connected my spots brown to yellow, blue to black and earth to earth.
This seems to work and I'm pretty sure now replicates exactly what was there before. The only concern I had was that the yellow had 75 volts when the switch was off and not connected to anything- it had 240 when switched on which is what you'd expect (?). Now that the yellow is connected to the brown on the spots, the voltmeter now shows the yellow with 5 volts when the switch is off.
Everything seems to be ok. Just seems a bit bizarre??
Access could be through floor above, but I may need to think about this to make access easier.
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Postby kbrownie » Wed Apr 15, 2009 6:18 pm

JohnnyC,
I'd stick with choc blocks rather than inaccessible junction box.
Two things as far as meter reading concerned.
Is the meter calibrated to prove reading is true and sometimes a small voltage can be induced via other live cables. Don't think it's a great concern.
KB
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Postby JohnnyC » Thu Apr 16, 2009 5:02 pm

Thanks KB
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