Issues tripping GFCI with variable speed pool motor.

Thread Starter

thatsmessedup

Joined Feb 15, 2018
56
I am a newly graduated electrical engineer with little practical engineering skills and my first gig. We plan to use signal phase, variable speed, permanent magnet pool motors that we have ordered in bulk, however they seem to spike about 15ma of common mode ground current when the motor turns on, tripping the class A (5ma) GFCI. I need a quick solution to fix the bulk order that we have and then a permanent solution that we can add to the motor for the next shipment.

From my research it seems like there may be a few options including isolation transformers, reactor, RC snubbers, common mode filter. But I really am not sure.

I am hopping that you guys have some helpful tips for me. Thank you!

This is the motor. I have more specs if needed.
1.JPG
This is the breaker.
2.JPG
And we have tried hooking it up in two ways shown below.
3.JPG
4.JPG
 

crutschow

Joined Mar 14, 2008
29,466
Did you measure the resistance between neutral and ground?

Otherwise it may be capacitive coupling between the hot and ground.
That could be difficult to eliminate.

Does it occur if you slow start the motor with the variable speed drive?
 

Thread Starter

thatsmessedup

Joined Feb 15, 2018
56
Did you measure the resistance between neutral and ground?

Otherwise it may be capacitive coupling between the hot and ground.
That could be difficult to eliminate.

Does it occur if you slow start the motor with the variable speed drive?
I do not have the motors with me and have not tested the impedance of ground and neutral but these are brand new. I have not tried to slow start the motor.
 

Thread Starter

thatsmessedup

Joined Feb 15, 2018
56
Try a by-pass of the breakers at switch on and see if they hang in.
After the by pass is removed.
They will work fine without the GFCI. In fact, if we use a 30ma gfci there is not problems at all. Its just that the standard we need to follow is class A which pops at 5ma ground current.
 

LowQCab

Joined Nov 6, 2012
1,914
Without a full and accurate Schematic, everything else is just guesswork.
And really, even a perfect Schematic is guesswork without an Oscilloscope, and extensive measurement.

A simple "Super-Fast-Diode" across the Motor may solve everything, and marginally increase efficiency.
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Thread Starter

thatsmessedup

Joined Feb 15, 2018
56
If the problem is common mode parasitic capacitances like the picture below, is there anything that can be done to remove the common mode current from tripping the gfci. This seems to be a problem among adjustable speed PWM motors. We measured the current in the ground to be about 50ma AC mostly around 15KHz.
5.JPG
 
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