floated voltage

Discussion in 'General Electronics Chat' started by superway, Jul 19, 2011.

  1. superway

    Thread Starter Active Member

    Oct 19, 2009

    Please se my hand drawing on attachment, why do I get floated voltage about 65vac betwwen the chassis of unit #2 and the ground of AC wall?


  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    could be that your supply is not correctly poloarized (Nuetral/L1), and likely that your chassis is not correctly bonded to supply outlet.
  3. someonesdad

    Senior Member

    Jul 7, 2009
    Could it be a phantom voltage? Use a VOM or load your voltmeter suitably.
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    The most likely explanation is that the wall outlet ground conductor is not continuous through the units.

    That should be simple enough to check. Disconnect the units from the wall outlet, leaving the rest of the connections as shown and do a continuity test (with a multimeter) between the #2 chassis and the wall plug (not the socket!) earth pin.
  5. superway

    Thread Starter Active Member

    Oct 19, 2009
    I might be added a wire between Neutral on Unit#1 to ground on AC outlet or the chassis #2 to AC outlet ground.
  6. radiohead

    Senior Member

    May 28, 2009
    I don't see a ground on either unit either. Test your AC outlet for correct wiring. You should get 120VAC from the small slot to the ground lug, and 120VAC from the small slot to the neutral long slot, and 0 VAC from the ground lug to the long neutral slot. Make sure the wiring through your units are correct and properly grounded.

    Furthermore, for testing AC circuits, I would recommend using a GFCI outlet for your source voltage.
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009

    your bonding should run parallel and continous with your AC line, connecting all chassis to ground. DO NOT connect your neutral to ground.
  8. SgtWookie


    Jul 17, 2007
    I'll assume that you're in the USA due to your 120v specification and the shape of the wall socket.

    Ground is connected to Neutral at the electrical service panel/breaker box/fuse box, but that is the ONLY place that they should ever be connected together. Ground is to protect people, not to be used as a power return. If there is a fault in an electrical device, the ground is supposed to keep the chassis at a 0v potential.

    If the fault is line (hot) to chassis ground, the circuit breaker or fuse will interrupt the mains power. If it is a GFCI-protected outlet and there is current through the ground wire above around 10mA, the GFCI breaker will trip.

    If there is no current being used in a circuit, you should measure 0v between ground and neutral. However, if there is a load on the circuit, you might measure a volt or so difference, depending upon how heavy the load is, and how long the length of wire is from the service panel to the load. If there is more than a couple of volts difference, you have a problem somewhere.