Voltage readings

Discussion in 'Electricians' Talk' started by Anthony McGrath, Nov 22, 2021.

  1. Went round to a friend's house as they had lost all power to lights when moving a switch. Found out that he had not put the feed into the junction box under the step, so rectified this. However when testing the circuits I got some strange readings and wonder if anyone can shed some light on them

    At a light fitting (the only one I managed to test as he is getting the place reboarded and plastered) I got 240v between line and neutral when it was turned on, but still got 65v when the switch was in the off position (same reading with two different switches). I was also getting voltage 110v between line and earth and around 90v between neutral and earth.

    I then disconnected the feed at the junction box (that we are assuming goes straight to the consumer unit) and I was getting 240v line to neutral, 100v line to earth and 95v neutral to earth.

    The wiring is very poorly done with cpcs not connected in most junction boxes, etc so there is no continuity of CPC.

    Insulation resistance test all came out at maximum 999.

    It has confused me how insulation resistance results are so good but yet there are strange voltage readings

  2. MGW

    MGW Screwfix Select

    Ohms per volt of multi-meter means not adding up to 240 volt, and clearly lacking earth.

    I had same with a house on the Falklands, and realised joints in loft space and no loft hatch.

    The problem is your now last to work on the property, so a watch your back exercise. Need to inform owners in writing how bad it is. Email, letter, text, fax does not really matter but in writing.
  3. The Happy Builder

    The Happy Builder Screwfix Select

    They need to stop boarding and sort the wiring out before completing it.
  4. Bazza

    Bazza Screwfix Select

    If you were using a simple multimeter you may have been just been picking up induced voltages.
    The general purpose multimeters are very high impedance and can mislead you. Test again with a shunt load across the leads, or use a proper electrical test device.

    If needs proper investigation. I agree with HB:

  5. Cheers bazza. Unfortunately I was testing with a Megger 1720, so presume I was getting correct readings. I rounded the 99.9 to 100

    Attached Files:

  6. Cheers

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