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Ground fault

Discussion in 'Electronic Basics' started by trickyrick, Jun 23, 2007.

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  1. trickyrick

    trickyrick Guest

    Good day
    I have a little problem with my ground fault always tripping.

    I have an above ground pool with a 1hp pump. I have a wire in a
    conduit to the pump. The wire is 14/2 and is about 100 ft from the
    panel. The pump will run for about 3 to 4 hours and then the breaker
    will trip. I have metered the wire and there are no grounds or
    shorts. The only thing that I can think of is maybe the size of the
    wire. I did unfortunately run the pump before with out any protection
    and the breaker never tripped.
    Any suggestions on what might be the problem
    Thanks
    Rick
     
  2. Tom Biasi

    Tom Biasi Guest

    There are really only three reasons this breaker will trip.
    1. You are overloading the breaker.
    2. You have uneven hot/neutral current flow. (ground fault condition.)
    3. Its defective or miswired.

    Tom
     
  3. Chuck

    Chuck Guest

    I assume you're in the US.

    Overload is unlikely if the only load is
    a 1 hp motor. The breaker is at least 15 A?

    Defective is always a possibility with
    GFCIs, but the circumstances under which
    it is tripping don't seem to match the
    time constants likely to be found in the
    device.

    The regularity of the tripping and the
    fact that it trips after being under
    load for 3 hours strongly suggests heat
    as a factor.

    Heat inside the GFCI is possible if the
    connecting wires don't make good
    electrical contact. I would not expect
    GFCIs to be very sensitive to heat.

    Heat inside the motor could easily cause
    expansion of a conductor with consequent
    shorting to the motor's case. Measure
    resistance from hot wire to case with
    the motor cold and it may be hundreds of
    megohms. When hot (immediately after
    removing ALL power after a trip) it may
    drop to 25,000 ohms or less. If so, it
    will cause at least 5 mA to be returned
    through the ground wire, thus causing
    the GFCI to trip. That's what I would
    look at first. Let it run till it trips
    and then remove all power and measure
    leakage resistance.

    Good luck.

    Chuck
     
  4. trickyrick

    trickyrick Guest

    Ok thanks
    Lets say it was an over load if that was the case would the pump run
    for about 3 hours before it triped
    If it was a ground fault condition would I not see some kind of ground
    on the hot or neutral side ( I see nothing)
    If it was misswired would it not trip right away
    Thanks
     
  5. Tom Biasi

    Tom Biasi Guest

    The overload could take place when the motor is hot.
    It would be hard to measure the ground fault since trip will take place with
    very little flow.
    The miswire probably would trip right away unless you did something weird.

    When you say it runs for 3-4 hours, is that after you have been splashing
    around in the pool?

    Tom
     
  6. Jasen

    Jasen Guest

    Did you use an insulation tester? a cheap VOM won't find all faults.
    cable insulation not waterproof?

    Bye.
    Jasen
     
  7. trickyrick

    trickyrick Guest

    Thanks guys for the input
    I will check for grounds today when it trips and let you know what I
    find
     
  8. ehsjr

    ehsjr Guest

    Kill power and look for crud/dirt in all involved
    junction boxes.

    Ed
     
  9. trickyrick

    trickyrick Guest

    Ok I waited around for a couple of hours until the pump tripped the
    breaker (15 amp ground fault) . I checked both the hot and neutral
    side of the plug for a ground and nothing (my meter goes to 3 million
    ohms).
    There are no junctions between the breaker and the pump. This is a
    new pump only 3 weeks old (1 hp). The one from last year sized up
    (bearings got wet) I could not get it going this season and even the
    old pump did it last year about half way through the season. Any
    other suggestions guys
    Thanks
     
  10. Eeyore

    Eeyore Guest

    Yes.

    How much current does it draw ?

    Not watts, not hp but AMPS.

    Graham
     
  11. Lord Garth

    Lord Garth Guest

    Additionally, the startup surge can be enough to trip a GFI. Another
    typical cause is if there is a 3-way on the same circuit.

    What does your meter indicate when you probe ground to neutral?
     
  12. trickyrick

    trickyrick Guest

    It' cant be the startup as I said in the original post the pump runs
    between 2 and 3 hours before i trips. This is the only thing that is
    on the GFI not even a switch.
    When I check ground to neutral its over 3 million ohms
    Rick
     
  13. Lord Garth

    Lord Garth Guest

    Read the AC volts between the ground and neutral. It should be very nearly
    zero however, I have measured 70 volts here. A new ground solved the
    problem.

    The 3-way can be ahead of the GFI rather than behind it and cause trouble.

    Something is causing an imbalance in the current between the hot and the
    neutral.
    That is what trips the GFI. Assuming the GFI isn't defective, there must be
    a
    path to ground somewhere.
     
  14. Eeyore

    Eeyore Guest

    Can you PLEASE check the current draw when it's contuously running ?

    Graham
     
  15. default

    default Guest

    Think of the pool as one plate of a capacitor to ground - may be no DC
    path to ground but that doesn't mean there isn't some leakage from the
    pump to the water - through the water to the pool - across the pool
    membrane to ground. AC only circuit.

    Check the resistance between hot and neutral to the water.
     
  16. default

    default Guest

    Another thought on the idea of current flow through the water being
    pumped - there may be air voids in the piping that occur when the pump
    is off preventing an honest ohm meter reading.
     
  17. @(none)

    @(none) Guest

    Remember that three things can trip a GFCI:

    leakage currents that bypass the neutral
    defective GFCI
    excessive current drawn

    Too bad the resistance test was negative. Doesn't necessarily mean there
    was no leakage. It gets more complicated from this point on. I still
    suspect heat because of the time constant. Could be a plugged filter
    that reduces water flow thru the pump and causes the motor to overheat.

    You can measure the AC current drawn by the motor, by please do be
    careful since your test leads will be hot.

    You can also measure the AC leakage current in the ground wire. But be
    extra careful if you do that, especially if leakage is a real possiblity!

    It might be easiest to start by either replacing the GFCI with a known
    good one, or routing your pump circuit to a different one.

    Use extra caution in all of this.

    BTW, did you say if you reset the GFCI it will run for another 2-3 hours?

    Chuck
     
  18. Doug Miller

    Doug Miller Guest

    Let's clarify, shall we?

    Overcurrent will trip a GFCI _circuit_breaker_ -- but that's because it's a
    circuit breaker, not because it's a GFCI.
     
  19. Eeyore

    Eeyore Guest

    If it runs for say another 15 mins and trips again, then the fault is likely to be a
    small overcurrent on the circuit.

    Graham
     
  20. Eeyore

    Eeyore Guest

    Well...... if the bearing getting wet caused the bearing to seize, it's
    reasonable to assume that before they seized they became 'tight'.

    If they did that, the motor would have to work harder (drawing more current) and
    that could cause an overcurrent trip of the breaker, i.e. nothing to do with a
    ground fault at all. I see that 1 hp pumps can draw ~ 11A so a modest 'overload'
    could indeed do it.

    Graham
     
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