voltage detector vs cheap chinese pedestal fan

Discussion in 'Electronics & Electrics' started by fR33z3, Jan 23, 2016.

  1. fR33z3

    fR33z3 Member

    Joined:
    Jul 16, 2001
    Messages:
    2,164
    Location:
    Perth
    Hey guys.

    Mrs bought and assembled a cheap chinese $10 pedestal fan this evening. Having added a non-contact AC voltage detector to the toolbag recently, I thought I'd do some basic checks.

    I am slightly concerned that the fan cage itself shows up as hot.

    Now if i remember correctly, the cage was clamped in place by plastic components, so I'm assuming this is an induction-coupling. However, I have another cheap fan, and it gets a zero reading from the detector.

    Anyone have a theory or explanation?
     
  2. aL4n

    aL4n Member

    Joined:
    Aug 18, 2003
    Messages:
    714
    I will not believe a volt stick, I only use it as a last measure and that's rare. If you want to test put a set of probes onto it.

    Some detectors are more sensitive than others, they will usually have it marked on the device how many volts it can pickup
     
  3. Dice

    Dice Member

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    Feb 18, 2002
    Messages:
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    Location:
    Altona
    They're often called deathsticks because they're not accurate nor trustworthy, and are a guide only.

    To be sure, get a decent multimeter, find a known earth (power point earth, for example, tested against 240), and test for voltage between known earth and exposed metal on cage.

    Anything else is frippery.

    (ie, set meter to a voltage range exceeding 300v AC;
    test between socket outlet earth and active;
    test between socket outlet earth and exposed metal of cage;
    test between socket outlet earth and active again)
     
  4. RobRoySyd

    RobRoySyd Member

    Joined:
    Jan 24, 2008
    Messages:
    8,236
    Location:
    Sydney
    The cheap non contact voltage detectors give false positives. I have several including ones sold by Jaycar and an Au on-line electrical trade supplier. All they're detecting very crudely is the presence of an electric field. The only one I have worth being in the toolkit is made by Fluke.

    You're right, induction is the problem.

    The correct procedure for testing a double insulated appliance is to tightly wrap the whole thing in alfoil and then measure the resistance between both the active and neutral pins of the plug and the foil at 500V. A multimeter is useless for this, you need an insulation tester, PATs include one.

    The above test however is not exhaustive because the device is not powered. Ideally the same test should be repeated with the unit powered up and operating.
     

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