measuring house amperage without breaking the circuit

Discussion in 'The Projects Forum' started by davevarga, Nov 30, 2008.

  1. davevarga

    Thread Starter New Member

    Nov 30, 2008
    How can I measure amperage on individual electric lines in the circuit breaker box in my house (without breaking the circuit?)

    I wanted to conjure up something homemade and put about 20 wraps of thin coated telephone wire around one of the conductors of the line I wanted to measure. I then put a multimeter on either end of that telephone wire, measuring microvolts AC. However I read nothing. Should I put a resister in series with the wire and measure across there?

    I figure if it worked, I could calibrate the voltage read with the current drawn through a lampcord (coiling around just the hot wire in the lampcord) and map the number of coils with the voltage shown with the amps drawn with a 100 watt bulb burning.

    But... my idea is flawed as it shows no voltage.

    Any ideas on how to measure amperage wtihout breaking the circuit on the electric line?


  2. hgmjr

    Retired Moderator

    Jan 28, 2005
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    Here is a link to an outfit that sells clamp-on current transformers -

    They aren't cheap and the measurement inside the breaker panel is somewhat dangerous. If this is just for curiosity, you can get a device called a Kill-a-Watt for less money that will plug in an outlet and let you monitor current much more safely.
  4. leftyretro

    Active Member

    Nov 25, 2008
  5. floomdoggle

    Senior Member

    Sep 1, 2008
    Easier than buying a tool, watch your meter. Turn off, or unplug all other electrical devices to that circuit and watch you meter spin. If it is only about the amperage, look at the device, you should have a plate on there stating the wattage.