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Discuss 200V DC coming down neutral from a bathroom fan? in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. Mattja
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    Mattja Active EF Member

    Location:
    UK
    I was looking for an insulation resistance problem (house full of crap and owner insistent on not getting a full rewire done, just replace the problem parts), and I found that the old bathroom fan is switched from the downstairs lighting circuit (bathroom light switch connects to the timer-control of the fan) and is powered by the rear-socket ring.

    Looking for insulation problems on the rear socket ring I found the problem to be at the fan, but the weird thing to me is that I found a 200V Direct Current, not AC, between the neutral and earth coming out of the fan. This occurred only when the bathroom light was switched on (just the rear-socket ring being disconnected at the time).

    I'm going to be replacing this bathroom fan of course, but I just wondered if anyone could shed some light on why it would be sending a DC voltage back down the neutral, but only when the Line from the lighting circuit is supplying power to the timer.
     
  2. PEG
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    PEG Trusted Advisor

    Location:
    Manchester
    hi bud,how are the circuits discussed,separated,in the DB,and what were you measuring voltages with? :)
     
  3. Mattja
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    Mattja Active EF Member

    Location:
    UK
    I had the fuse taken out for the rear-socket ring and the neutrals for it taken out of the neutral bar and put in a wago, earth still connected. Using a KT65 multitester.
     
  4. RWJ
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    RWJ 8,330 day wonder Electrician's Arms

    Location:
    East Anglia

    So the neutrals aren't connected? If not then they are not neutrals are they!!
     
  5. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    If I read your OP correctly you are saying the fan is connected across 2 circuits (?) being Light for switching and RFU for continuous power. I'd probably fix that first and see what happens.
     
    • Agree Agree x 5
  6. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Ha - a little plug for the Rugby Football Union :)

    IMG_0723.JPG
     
  7. Mattja
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    Mattja Active EF Member

    Location:
    UK
    Yes RWJ *eyes rolling spectacularly* but everyone knows what is meant and it's far less of a mouthful than "the terminal where the neutral is to be connected", can we move on?

    I agree Wilko, going to be putting a 3 core & cpc in where the single is currently running from the light switch to the timer.


    Not got an issue putting a new fan in (there's the insulation problem regardless), just curious about how there's a 200V DC voltage coming out of the neutral terminal of the old one when a live AC is connected to the timer. Hoped someone here may be learned in the ways of the fan.
     
  8. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Never seen that one before, but perhaps it's from the electronics in the timer, which will create DC to run itself. 200V doesn't sound toooo healthy, but fix up the wiring and it might come good. Me being hopeful :)
     
    • Like Like x 1
  9. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    How have you identified it as being DC and not AC? Depending on the method of measuring this it could be as simple as a rectifier circuit in the electronics causing the meter to record a DC voltage.
    If I have read this correctly you have disconnected L&N and just left the S/L connected and live? Which apart from being downright dangerous is liable to give unexpected or unusual voltage readings from both disconnected terminals.
    Without all terminals properly connected your voltage readings are likely to be a nonsense and should be ignored.
     
    • Like Like x 1
  10. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    What is wrong with the bathroom fan that it needs replacing?
     
    • Agree Agree x 2
  11. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Why do you think there is an insulation problem?
     
  12. DPG
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    DPG Electrician's Arms

    Location:
    S Yorkshire
    I wondered this too. Surely the problematic readings were caused by the wiring configuration.
     
    • Agree Agree x 2
  13. RWJ
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    RWJ 8,330 day wonder Electrician's Arms

    Location:
    East Anglia
    I thought it was a fair question obviously "arrogant eye rolling spectacularly" it wasn't
     
    • Like Like x 1
    • Funny Funny x 1
  14. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    I think #5 has said the best way forward, reinstall the fan circuit and retest.
     
    • Like Like x 2
  15. b-spark
    Offline

    b-spark Regular EF Member

    Never seen this, but if you have measured correctly, sounds like a bridge rectifier and your measurement is across it. What are the lights???
     
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