clamp meter theory

Discussion in 'General Electronics Chat' started by strantor, Apr 10, 2012.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
    1. Does measuring current with a clamp meter cause the meter to draw more power? In other words, if the meter is on but no conductor is inside it's clamp, does it draw less power than if it were on and there was a current carrying conductor inside it's clamp?

    2. Does measuring current with a clamp meter cause more power to be drawn from the source? Meter loading. For example, you measure the current going to your dryer, does the presence of the meter cause more current to be drawn, even a very tiny bit?

    3. If the answers to 1 and/or 2 are 'yes', is it possible that, if you had a mains-powered clamp meter, and you used the clamp meter to measure it's own current, would the current drawn increase exponentially due to the perpetual positive feedback, until the breaker tripped?
  2. jimkeith

    Well-Known Member

    Oct 26, 2011
    1. no difference in meter battery power on or off active conductor, but does receive power from conductor

    2 yes, meter draws a little power from source--actually puts small impedance in series with load

    3. or blows up the meter :) (overunity topic not allowed!) LOL

    Do not hold meter in hand!
    Last edited: Apr 10, 2012
    strantor likes this.
  3. #12


    Nov 30, 2010
    An amp-clamp works by putting the suspected current carring wire inside its magnetic steel as a "half turn". The power for the meter comes from the current carrying conductor. No amplification happens in the meter. It still works without batteries in it.

    ps, great way to make an amp-clamp last 30 years: Don't put batteries in it. When the batteries don't corrode, the clamp meter doesn't rot from the inside.
  4. gerty

    AAC Fanatic!

    Aug 30, 2007
    FYI: In case you didn't know, wrapping the current carrying conductor two turns around the clamp jaws wil result in a double value reading. Useful when current values are very low, just divide reading by 2 for true value.
  5. #12


    Nov 30, 2010
    I do that with 10 turns to make the math easy :)
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    The AC clamps are usually just a current transformer..
    Many of the AC/DC clamp on ammeters feature a split iron/ferrite core and that focuses the magnetic field from the wire you are measuring on a hall effect sensor mounted between the bottom split.