7.5 hp 230 volt trips 60 amp GFCI breaker

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@ stephenweyant,

Approximately what are the lengths of the branch circuit wiring, for the 3 pump motors, from the 2P 60A GFCI breakers to the motor/controller?

What size of wire was installed? #8awg or #6awg.
I assume + EGC wire installed.

I assume the electrical panel is single phase 120/240V 3wire.
Same for the electrical service, 120/240V 3wire?

Have you checked or hired anyone to check any of the 3 motors winding for winding insulation resistance leakage to ground from each of the 2 motor leads?

http://www.techni-tool.com/site/ART...te Guide to Electrical Insulation Testing.pdf
 
@kwired

thanks for that info kwired. I did read up on the NEC regarding GFCI and its listed in art. 100 regarding the UL 943 Standard for Ground-Fault Circuit Interrupters.

the GFCI device I was looking at is rated 10mA through 100mA UL1053 and is considered a ELCI. so I don't feel this will work.

so we are back to the beginning!
 
@jamesco

thanks for your questions jamesco

just to clarify, these are 3 isolated incidents at different locations all together.


the distance from breaker to motor is less than 20'

the wire size is #8 or #6 THHN, I don't recall. the motor FLA is 30.4 so 125% still falls under 40 amps.

I don't recall if the main panel is 3 wire or 4 wire but it is 120/240 volt

voltage leakage through the motor windings was a thought but all three motors? its possible! we were thinking of wiring up a brand new motor to test this as we have one on hand.
 
stephenweyant said:
@jamesco

thanks for your questions jamesco

just to clarify, these are 3 isolated incidents at different locations all together.
Click to expand...
Yes, I understood from your posts, 3 different locations.

the distance from breaker to motor is less than 20'
Click to expand...
That rules out my thinking maybe it was an induction or capacitance issue during initial high inrush current on the branch circuit wiring, causing an imbalance on the 2 ungrounded conductors which might be causing the sensing coil in in the GFCI to trip open. 20' is nothing

the wire size is #8 or #6 THHN, I don't recall. the motor FLA is 30.4 so 125% still falls under 40 amps.
Click to expand...
Even using NEC 430 to size the branch circuit wire #8 is all that is needed. 20' is short.

I don't recall if the main panel is 3 wire or 4 wire but it is 120/240 volt
Click to expand...

voltage leakage through the motor windings was a thought but all three motors? its possible! we were thinking of wiring up a brand new motor to test this as we have one on hand.
Click to expand...

Common denominator? Same motor manufacture. By chance have you tried to contact the manufacture directly about your problem? Speak to an EE?
- Three different pump locations.
- Branch circuit wiring length is approx 20'.
- All 3 GFCI breakers are CH.

- The breaker is slightly sized less that 200% of the motor FLA name plate rating. Motors start up fine, every time, when using a standard 2P 60A CH breaker.

- The motors are installed at 3 different locations.


Can it be the CH GFCI breaker that is at fault? Possible.

But I believe you stated in your thread the manufacture is/has had complaints of their motors causing GFCI breakers to trip open on start up.

Is it the insulation resistance of the start winding breaking down/leaking voltage, ever so small to cause at least a 5ma or 6ma current to flow to case/frame of the motor, during the high inrush current through the start winding when the motor is trying to start?
IF not could it be the start capacitor MFD selected by the manufacture that is causing a leading/lagging PF on the branch circuit causing the sensing loop in the GFCI to trip the breaker open?

This may sound dumb. If the conduit for the motor branch circuit wiring is big enough pull the wires out, (at just one of the 3 pump locations) and twist the 2 hots together keeping the twisted maintained from the breaker to the motor controller. As for the EGC wire do not twist it with the 2 hots. Just pull it back in straight along side the 2 twisted hots.


.
 
good info again jamesco

so two of the motors are identical, US Motors 7.5 hp using 4 round (start) caps and one oval (run) cap. the third motor is an AO Smith 7.5 hp using only two round caps.

Im thinking its got to be one of the following

1. breakdown of insulation in motor windings allowing voltage leakage
2. imbalance on start up caused by in rush current
3. something to do with capacitors

I am currently trying to contact cutler hammer and us motors to see what they think. meanwhile we will take a new US motor and wire it up to the cutler hammer gfci breaker. we will also use another manufacturers gfci and see if it trips. I have a megger insulation tester to make sure the motor windings are good too.

twisting the wires together will create induced voltage or cancel it out?
 
stephenweyant said:
good info again jamesco

so two of the motors are identical, US Motors 7.5 hp using 4 round (start) caps and one oval (run) cap. the third motor is an AO Smith 7.5 hp using only two round caps.

Im thinking its got to be one of the following

1. breakdown of insulation in motor windings allowing voltage leakage
2. imbalance on start up caused by in rush current
3. something to do with capacitors

I am currently trying to contact cutler hammer and us motors to see what they think. meanwhile we will take a new US motor and wire it up to the cutler hammer gfci breaker. we will also use another manufacturers gfci and see if it trips. I have a megger insulation tester to make sure the motor windings are good too.

twisting the wires together will create induced voltage or cancel it out?
Click to expand...


twisting the wires together will create induced voltage or cancel it out?
Click to expand...

Cancels induced voltage.

Inrush current in the 120 -130 amp range, as I believe you stated you measured using a standard 2P 60A breaker, will create a pretty good magnetic field around each of the 2 hot current carrying conductors.

When the conductors are pulled loosely/randomly in the conduit with the insulated EGC wire the magnetic field from the two current carrying conductors will induce a voltage onto the EGC wire.
 
stephenweyant said:
good info again jamesco

so two of the motors are identical, US Motors 7.5 hp using 4 round (start) caps and one oval (run) cap. the third motor is an AO Smith 7.5 hp using only two round caps.

Im thinking its got to be one of the following

1. breakdown of insulation in motor windings allowing voltage leakage
2. imbalance on start up caused by in rush current
3. something to do with capacitors

I am currently trying to contact cutler hammer and us motors to see what they think. meanwhile we will take a new US motor and wire it up to the cutler hammer gfci breaker. we will also use another manufacturers gfci and see if it trips. I have a megger insulation tester to make sure the motor windings are good too.

twisting the wires together will create induced voltage or cancel it out?
Click to expand...
Twisting supply wires together probably has little effect on only a 20 foot long circuit.

My guess is there is enough leakage somewhere within the motor due to capacitive or inductive effects, keep in mind the current is much higher at the moment it starts to turn the rotor then it is a full load rating, does not last long but if enough leakage is present to trip GFCI it will never get past that point even though the leakage very well may be much less at normal running speed and load conditions.

Other motors may have sampe problems but only those used for swimming pools are being noticed as they are about the only ones used with GFCI's.
 
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