Gfci tripping when pump turns off?

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glene77is

Senior Member
Location
Memphis, TN
Any idea why the gfci would trip when the spa motor is turned off? Will start and run. Trips when motor is turned off. Can anyone think this one further than me?
Try this.
The collapsing magnetic field of the motor is sending a spike down the line.
This spike (with a high frequency edge) is capacitively coupled into the electronic circuitry of the GFCI,
causing a mis-read of the 'balanced' state of the hot/neutral current picked up by the sensing toroid.
Try putting a light-bulb on the circuit to maintain an alternate path for the spike.
Just a thought. :)
 

electricblue

Senior Member
Location
Largo, Florida
Try this.
The collapsing magnetic field of the motor is sending a spike down the line.
This spike (with a high frequency edge) is capacitively coupled into the electronic circuitry of the GFCI,
causing a mis-read of the 'balanced' state of the hot/neutral current picked up by the sensing toroid.
Try putting a light-bulb on the circuit to maintain an alternate path for the spike.
Just a thought. :)
Shouldn't the motor capacitor absorb this spike?
 

a.bisnath

Senior Member
gfci outlets are sometimes problematic

gfci outlets are sometimes problematic

In my over 20 years as a field electrical guy i have met numerous problems with all kinds of gfci outlets, sometimes its ants,moisture or as is described 'the gfci is getting weak" many years ago with the toroid and passive electronic components they were possible be repaired and be reliable ,even recertified,the newer one with semiconductors are not so
.Comes back to what was said above replace it and see
 

glene77is

Senior Member
Location
Memphis, TN
Shouldn't the motor capacitor absorb this spike?
Possibly, but if it is a capacitor start, then the cap will be switched out of the circuit.

In my mind's eye, I see the impedance of the start winding
prohibiting the shutdown spike from returning back through the cap,
connected or not.
Thus the spike must dissipate down-stream, into the GFCI.

The 60 cycle circuit will have a calculated impedance difference
of about .017 % that of a DC circuit.
The "run winding" and "start winding" work in this range.
Whereas, the spike from the shutdown
may have a rise time of .0001 second (aprox),
which will appear to be a 10 KHz signal (aprox),
which will be impeded by the start winding.
Thus the spike must dissipate down-stream, into the GFCI.

In a practical application of this concept,
where electronic components are involved,
a control board with a contactor relay
has a coil which requires a shut diode
to allow the discharge spike to bypass the coil (in reverse direction).
The impedance of the operating coil will impede the discharge spike
due to the high frequency characteristics of the spike.
This shunt diode keeps the spike from reaching electronic components on a circuit board.

In your application,
you need to prevent the spike from reaching the GFCI circuit board.

HTH, :)
 
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GUNNING

Senior Member
Upsell

Upsell

How bout replacing the receptacle with a breaker? Might have a staple in the wire too far, look near the motor and meg it out.
 
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gar

Senior Member
101214-0756 EST

From the description of the problem is seems clear that a voltage transient from turn off of an inductive circuit is causing the trip.

Motor capacitors are not going to minimize this transient. However, external capacitors of the proper type and value in combination with inductance, namely an appropriately designed filter, will reduce or eliminate the problem. An MOV at the motor might help, but it is simply a soft peak voltage limiter. An MOV does not reduce the rate of rise of the transient until it starts to clip the transient.

I have tested a Leviton 7899 GFCI with a crude transient generator, an AB #2 motor starter, rapidly and randomly actuated, and been able to trip the GFCI. It does not easily trip, meaning the probability is low, but possible.

In general I consider the 7899 relatively immune to transient tripping. However, looking at their circuit board layout I can see an easy change that might further improve its immunity.

.
 

ELA

Senior Member
101214-0756 EST


I have tested a Leviton 7899 GFCI with a crude transient generator, an AB #2 motor starter, rapidly and randomly actuated, and been able to trip the GFCI. It does not easily trip, meaning the probability is low, but possible.

In general I consider the 7899 relatively immune to transient tripping. However, looking at their circuit board layout I can see an easy change that might further improve its immunity.

.
If you used a Electric Fast Transient generator to test you get very repeatable results at tripping GFCI's.
Older units were more susceptible than newer ones.

I think the immunity level is somewhat a tradeoff with trip time. Curious how you would improve the immunity without affecting trip time? Of course there is always the cost factor as well :)

Both AFCIs and GFCI's could be much improved , at a cost.
 

gar

Senior Member
101214-1100 EST

ELA:

The problem area I see on the Leviton board is a somewhat long trace from pin 1 of the LM1851 to the SCR gate. No resistor in the trace path and the shunt capacitor is at the 1851.

The capacitor C2 should be moved to a spot immediately adjacent to the gate and cathode terminals of the SCR. Then a small resistor, maybe 1000 ohms, should be in the trace from the 1851 to the SCR gate, and adjacent to the SCR gate. This would reduce stray capacitive coupling to the SCR gate.

This particular problem area has nothing to do with the inverse trip time characteristic of the 1851.

.
 

ELA

Senior Member
101214-1100 EST

ELA:

The problem area I see on the Leviton board is a somewhat long trace from pin 1 of the LM1851 to the SCR gate. No resistor in the trace path and the shunt capacitor is at the 1851.

The capacitor C2 should be moved to a spot immediately adjacent to the gate and cathode terminals of the SCR. Then a small resistor, maybe 1000 ohms, should be in the trace from the 1851 to the SCR gate, and adjacent to the SCR gate. This would reduce stray capacitive coupling to the SCR gate.

This particular problem area has nothing to do with the inverse trip time characteristic of the 1851.

.
Have you tested your theory or is it all speculation?
My experience with EFT and EMI is that ICs are often upset by the high frequency components of the transient. It may have nothing to do with the SCR gate false firing directly. The 1851 may get upset and falsely command the SCR to fire. In that case the changes you mention would not matter.

Only testing using a repeatable test methodolgy would prove what the susceptibility issue is.

In my experience this often involved improving the ground plane.
 

gar

Senior Member
101214-1515 EST

ELA:

What I suggested may not be the problem, and I have made no effort to determine if this change would reduce the probability. Although it would not be too hard to do a simple experiment I do not choose to solve Leviton's problems for free. However, my suggestion might make a difference in the probability of triggering, and also your suggestion of a ground plane is very good.

I do not have the equipment to do a controlled transient voltage test, and therefore, I use what is available.

.
 
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