Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dishwasher - Voltage at metal cover

  1. Sep 2, 2006 #1
    My dishwasher in the kitchen has a metal cover inside and some persons got a small electric shock when they touched the metal cover with wet hands.

    So I took a voltmeter and measured the voltage between the metal cover of the dishwasher and the metal-washbowl (I suppose the metal-washbowl is on ground). I measured an AC voltage of 26.7 V (Note: the dishwasher is turned off).

    [metal-washbowl] <--- Voltmeter ---> [ metal cover inside of dishwasher]

    Has anyone else here experienced something similar? Or have an explanation for this?
  2. jcsd
  3. Sep 2, 2006 #2


    User Avatar
    Gold Member

    Unplug the sucker and have it serviced! There's something wrong for sure, and it's potentially fatal. If you get even a tingle from something on household current, don't mess with it. The thing isn't properly grounded. There's no way to know specifically what is causing the problem as far as the circuitry goes, but the chassis should be attached to your 3rd prong to prevent this sort of thing.
  4. Sep 3, 2006 #3
    If the dishwasher was off and you still get a voltage from chassis to ground there could be a problem with the neutral. It may be bonded to ground somewhere creating a loop in the grounding system.
  5. Sep 4, 2006 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I agree. This means the neutral wire is somehow compromised. Turn off the entire circuit in you breaker box, and do not use the appliance until you've had an electrician investigate.

    - Warren
  6. Sep 5, 2006 #5


    User Avatar
    Gold Member

    Neutral is supposed to be bonded to ground. These stray voltage problems arise primarily when neutral is not properly referenced to ground. When this happened in our old house a heavy load energizing on one leg would shift the potential of the neutral, pulling down the voltage on that leg, and increasing the voltage on the other leg. For example, when the refrigerator cycled on, some lights would get brighter and some would dim, depending on what leg of the 120Vac they were on. The problem was a loose clamp in the breaker box. Once I tightened the clamp, neutral was once again properly connected to ground, and the problem went away.

    To the OP - don't play with this stuff yourself. Get an electrician to check it for you.
    Last edited: Sep 5, 2006
  7. Sep 5, 2006 #6


    User Avatar
    Science Advisor
    Homework Helper

    There are such things as ground loops.
    They can be very nasty.
    This could be an example of improper bonding to ground.

    To the OP
    Whatever the actual problem is.
    Find someone to fix it before you get killed.
    You should check your other electical appliances a well.
    It may not be only the dishwasher that has the problem.
  8. Sep 5, 2006 #7
    Edgardo, The metal frame of the dishwasher is not bonded to ground or the green wire has lost continuity to the distribution panel. Make sure there is a mechanical connection between the green wire and the metal frame of the dishwasher. Make sure the green wire has continuity to the ground connection point at the distribution panel. Ground and neutral are bonded at the distribution panel. I work as an industrial electrician and see this condition somewhat frequently. If you ground the metal frame of the dishwasher the nuisance shocks will disappear.
  9. Sep 6, 2006 #8
    Thanks for all your replies. I didn't think it was that dangerous, but I will let this fix by an electrician.

    And indeed the dishwasher was not installed by a professional electrician.
  10. Sep 6, 2006 #9
    I am an electrician. The neutral is only bonded to ground at the main service, and nowhere else. Odd voltage problems are usually caused by problems with neutrals.
  11. Sep 6, 2006 #10


    User Avatar
    Gold Member

    Hey, another neighbour! Cool.
  12. Sep 6, 2006 #11


    User Avatar
    Gold Member

    Thank you. Neutral is only to bonded to ground at the entrance panel. That connection is not the only one that can deteriorate and cause a problem, though. The connection between the ground wire running to that entrance panel and the chosen gound point can also loosen or corrode. These can be a bear to chase down. It's far worse with industrial 3-phase power, but that's another story.
    Last edited: Sep 6, 2006
  13. Sep 6, 2006 #12
    I should have used the word "main service" rather than distribution panel. Whenever I hear complaints of non-electrical personnel getting shocked from a piece of equipment, 99.99% of the time I find 26-30VAC between the offending piece of equipment and another piece of properly grounded equipment they happened to be touching at the same time. I always find a missing ground in this situation. This sounded like your situation. If you have a stainless steel sink, this would have been a good ground provided you have metal water pipes and were touching both the sink and dishwasher at the same time. I believe this induced voltage is caused by capacative effects and some leakage.

    The only reason I open my mouth is to change feet.
  14. Sep 6, 2006 #13


    User Avatar
    Gold Member

    If you're trying to snipe my medal, get over to GD and do it up proper. :tongue:
  15. Sep 7, 2006 #14
    Pardon me Danger, I borrowed it from a post at Engineering Tips Forum. He may have plagiarized it from you. I must admit that it made me chuckle.
  16. Sep 7, 2006 #15


    User Avatar
    Gold Member

    No, I didn't mean that I ever said that; I didn't. I actually remember seeing it before, but can't remember who it was. I was just agreeing that it's funny.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Dishwasher - Voltage at metal cover
  1. Old Dishwasher Motor (Replies: 5)

  2. Metal detector (Replies: 1)

  3. Metal conductivity (Replies: 2)