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  1. #1
    Join Date
    Jan 2005
    Location
    greensboro
    Posts
    1
    can someone explain phantom/shadow circuits to me, because i chased one for about an hour before i figured out there was no true voltage in a carrier spit h.p. 12 ton system

  2. #2
    Join Date
    Oct 2002
    Posts
    970
    Are you talking about induced voltages on wires..Partial voltages on wires that aren't energized?
    I work with the Chiller Whisperer...

  3. #3
    Join Date
    Jul 2001
    Location
    Southern NJ
    Posts
    1,241
    If you're talking about phantom voltages:

    They come from several sources and they're real. The voltage your digital multi meter (DMM) shows is really there. but the power available is so low that that once any sort of tiny load is put on the wire, the voltage drops to nothing.

    Even a piece of wire with the ends attached to nothing can have a voltage difference between the ends, especially if it's next to an energized wire. The energized wire's magnetic field "induces" a voltage in the unconnected wire. If you put your DMM on both ends of ths wire, you'll get a voltage reading. But if you use an analog meter you'll see no voltage because an analog meter needs a little bit of current to move the needle and there's no real current available. DMMs are great but this is one of their down sides. DMM's have infinate internal resistance (or almost) and don't bleed off phantom voltages. If you're not sure if the voltage is real, use a wiggy type meter to test.
    Ryan
    Maintenance Guy
    -----------------
    naysayer, skeptic, conspiracy theorist

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