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Wiring Choice.

Zoomup

So there I was in the corner of a loft. I had two 1.0mm2 T&E cables to wire up for two new 240 Volt shower room ceiling lights that replaced some old 12 Volt faulty ones. The new ones covered the ceiling holes nicely. But, how to easily wire them in?

Ah, there is a convenient junction box that connects to the extractor fan, great I will just wire into that. It will have a permanent L which I don't need. It will have a N which I do need. And it will have a light switch controlled switch L which I do need. But wait, the grey and black are not sleeved or tagged with coloured tape. Is grey N or switched L? Is black N or switched L?

Well if it was installed by an old boy it is likely that black is N. But it may not be. If I wire up the lights reversed polarity they will still work but the install will not be compliant. I have no tester with me and the circuit is turned off while I am working on it. What did I do?

 

Z.

 

 

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    Read the Daily Mail?

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    Many possible options. Go home and get your test kit since you can't complete the job without testing it anyway probably should be top, in the middle you could have used the new lights as an impromptu test lamp - e.g. L to PE with various switch combinations to see if it either lights or trips an RCD or open up the switch or whatever the 3+E goes to to see what core colours have been used there. Bottom of the list would be using a pair of fingers on the same hand to detect voltages between two terminals (again with varying switch position).

       - Andy.

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    But you would have already carried out safe isolation so a tester won’t help you. 

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    Pop the rcd with a link to earth

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    aligarjon: 
    Pop the rcd with a link to earth

    Only if it's TT.

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    assume brown is steady live, and connect the lamps between black and grey?

    look at the fan end of the wiring,? What else is in the JB, surely it is not a join in the middle of the 3core and E ? If any other colours enter the box, you sh9ould be able to improve the odds on guessing polarity.

    Mike

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    Chris Pearson: 
     

    Read the Daily Mail?

    It is too dim to read in the loft Chris. You should know that.

    Z.

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    Colin Haggett: 
     

    But you would have already carried out safe isolation so a tester won’t help you. 

    Indeed.

    Z.

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    mapj1: 
     

    assume brown is steady live, and connect the lamps between black and grey?

    look at the fan end of the wiring,? What else is in the JB, surely it is not a join in the middle of the 3core and E ? If any other colours enter the box, you sh9ould be able to improve the odds on guessing polarity.

    Mike

    Yep, the junction box was just a join in the middle of the three core and earth for the fan.

    Z.

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    Answer. I had a gut feeling that the install was made initially by an old boy. So I connected up blue of the new cables to black of the fan wiring for N. I then connected up the new brown for the new lights to grey for switched L.

    After fighting my way down to the landing past the killer spiders in the loft, I went downstairs to the garage and reset the lighting M.C.B. Upon testing the now live lights in the shower room I was amazed that by chance I had chosen the correct combination of colours. The lights worked well via the pull cord switch………………well if the shower isolator switch was in the ON position. The convenient loft fan junction box was located post fan isolator switch not before it. Doh! Anyway after a bit of additional fiddling I get it all sorted. I do dislike lofts with the killer spiders, loft insulation, dust, limited light and tangles of wires.

    Anyway job done and customer paid.

    Z.

    P.S. Note to self. Do not connect loft lights to the upstairs lighting circuit.

     

     

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