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I was changing a light pendant today

  1. Dec 16, 2007 #1
    and considered doing this with just the switch turned off. After turning off the switch I checked the voltage with a meter in A/C mode. It was 140V which I thought a tad high. When I turned the switch on the reading was 230V as expected (in the UK). So I turned off the lighting circuit at the consumer unit which brought the voltage to less than 1V as expected. So what I can't work out is where the 140V is coming from ? All the lights work independently so I don't think it is a series wiring thing.

    Any ideas or trouble shooting tips ? This is the electricians forum isn't it ?

  2. jcsd
  3. Dec 16, 2007 #2
    I am not familiar with the types of circuits used in the UK, but if I saw a similar thing in the US (i.e., say 60VAC on a normal 120VAC line), I would be deeply suspicious of the neutral. In any event, that sounds like you need an electrician.
  4. Dec 16, 2007 #3
    I have a CCF light that dimly pulses (only visible at night) every several seconds when supposedly switched off but still plugged in, so I presume it must be the same problem (my multimeter has a flat battery just now though).
  5. Dec 17, 2007 #4
    If the meter measures 140V there is 140V. The meter has a high impedance ( 1M - 10 M ), so you need very little Amps to sustain that voltage.

    If you put a low resistance, say 10 KOhms, in parallel with the meter, youll probably get a very low voltage. If this is the case its all OK.

    This current can come from capacitance or coupled inductance between the wires.
  6. Dec 17, 2007 #5
    Household outlets should be able to provide quite a bit of current without a significant drop in voltage. When I run my microwave the voltage drop at the outlet is less than 5V. The microwave uses about 600W so its impedence is only about 24 Ohms. If you can repeatably get measurements at about 50% of what is the correct voltage for the outlet, then I'd agree with tvp45 and say you need an electrician.
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