refrigerator tripping GFI

[GoldDigger]

I think the leakage is downstream of some internal control on the fridge which has to be energized to work - either a solenoid or contactor type control - and that's why I got no continuity thru the cord cap

That would be completely consistent with the fridge working when it is first plugged in, but "randomly" tripping the GFCI at some later time.

 

[DaveBowden]

you're right. I didn't think about that. I think when I get back there I'll check for continuity between the fame of the fridge and the neutral blade on the cord cap. Maybe there's a bad connection on the unit's ground wire or something.

 

[Little Bill]

That would be completely consistent with the fridge working when it is first plugged in, but "randomly" tripping the GFCI at some later time.

you're right. I didn't think about that. I think when I get back there I'll check for continuity between the fame of the fridge and the neutral blade on the cord cap. Maybe there's a bad connection on the unit's ground wire or something.

But the OP said this:

Plugging in the refrigerator causes the GFI to trip immediately.

 

[jumper]

Nice catch Bill.:thumbsup:

 

[kwired]

I think the leakage is downstream of some internal control on the fridge which has to be energized to work - either a solenoid or contactor type control - and that's why I got no continuity thru the cord cap.

Could be. I think most of the time the compressor is directly controlled by thermostat, there is also the condenser and evaporator fans that would likely be connected directly to same place as compressor.

What else is left? You have interior lamps, defrost heaters, and defrost control, and ice maker equipment. If in an apartment there is likely nothing more to it, some maybe wouldn't even have defroster.

If the fridge is warm the thermostat would likely be calling for run immediately when energized. Defrost OTOH would depend on where in the cycle the defrost timer is.

 

[GUNNING]

I have seen hot fridge boxes before. Run your meter between a metal spot on the fridge and a grouned point. If you see voltage its live and you can prove the appliance is the problem.

 

[kwired]

I have seen hot fridge boxes before. Run your meter between a metal spot on the fridge and a grouned point. If you see voltage its live and you can prove the appliance is the problem.

You still have to convince the owner it is a problem, if it works otherwise. Remember this thing wasn't a problem before the GFCI was installed. If people are getting shocked it maybe makes more sense to them.

 

[ceb58]

4-6 mA from a receptacle type GFCI is different than 4-6 mA from a GFCI breaker?? The devices ability to filter out inductive kick back and other false trip conditions is more likely what is different about them.

My point is I have had on more than one occasion a motor with a capacitor start trip a GFCI receptacle and not trip a GFCI breaker. Its just a suggestion for the OP to try. If it works get paid and run. By this time he could have pulled a new circuit.

 

[GUNNING]

Gzzzap

Gzzzap

The reason nobody is getting shocked is there are no conductive surfaces around. Some of the culprits are ice on the connections in the ice maker where it plugs in to the back of the freezer or condensation ice on the light bulb socket or control board, or a frayed wire in the door. It happens, but shocking the owner to prove it is hot is not a good business model.:ashamed1:

 

[ceb58]

It happens, but shocking the owner to prove it is hot is not a good business model.:ashamed1:

No but it would make you feel better for the guy calling you a liar and acting like you don't know what you are doing.

 

[GUNNING]

happy dance

happy dance

Slows em down enough to write the check.:happyyes:

 

[Rick Christopherson]

Contrary to the popular statements on this forum, tripping a GFCI does not mean you have a true ground fault or even problem with an appliance. It means that there is an imbalance between the wires feeding that appliance. What is overlooked is that this imbalance can simply be related to the storage ability of reactive devices. The current entering does not equal the current leaving, because there is a time delay in the reactive components. If the GFCI device does not take this phase shift into account, it will trip with reactive devices.

 

[GoldDigger]

Contrary to the popular statements on this forum, tripping a GFCI does not mean you have a true ground fault or even problem with an appliance. It means that there is an imbalance between the wires feeding that appliance. What is overlooked is that this imbalance can simply be related to the storage ability of reactive devices. The current entering does not equal the current leaving, because there is a time delay in the reactive components. If the GFCI device does not take this phase shift into account, it will trip with reactive devices.

Any reactive components that can cause an imbalance between current in the hot and the neutral wire must offer an impedance path to ground, the other phase of an MWBC, or something else. Even if the reactive impedance is just the capacitance to air/ground of the refrigerator body.
Without that, there can be any type of mismatch between the phase of the voltage and the current at the GFCI, but no imbalance or phase shift between the current in the two current-carrying conductors. (Courtesy of Kirchoff's Laws)

 

[kwired]

Any reactive components that can cause an imbalance between current in the hot and the neutral wire must offer an impedance path to ground, the other phase of an MWBC, or something else. Even if the reactive impedance is just the capacitance to air/ground of the refrigerator body.
Without that, there can be any type of mismatch between the phase of the voltage and the current at the GFCI, but no imbalance or phase shift between the current in the two current-carrying conductors. (Courtesy of Kirchoff's Laws)

:thumbsup::thumbsup::thumbsup:

 

[hurk27]

Any reactive components that can cause an imbalance between current in the hot and the neutral wire must offer an impedance path to ground, the other phase of an MWBC, or something else. Even if the reactive impedance is just the capacitance to air/ground of the refrigerator body.
Without that, there can be any type of mismatch between the phase of the voltage and the current at the GFCI, but no imbalance or phase shift between the current in the two current-carrying conductors. (Courtesy of Kirchoff's Laws)

Not always so, two current sources can be out of sync of different frequencies that can cause an imbalance it is not a problem of the current sources returning to is source as in Kirchoffs Law, it is a problem of what the current coil see's in a given instance of time, if we look at an inductive kick back on a circuit with a 60hz current on an O scope we can see that there is a spike of a very short duration that can be out of sync with the 60hz current, it can be an additive or subtractive to the 60 hz voltage for just a very short duration that because of the sync problem will put additive current when the 60hz is cresting on the positive side of the cycle but not on the negative side, the inductive kick back can have a much faster rise time and decay, it is of a higher frequency that can imbalance the circuit that can cause the current transformer in a GFCI to develop voltage, most LM 1851 chips in most quality GFCI's have a small time delay of the UL max which I think is 25ms, this delay is to gate out the inductive kick back by delaying the electronics from looking for the voltage from the current coil for about just over 1 cycle, in most cases it is enough, but there are some cases where switch contact bounce might cause it to last longer then this will trip the GFCI.

Many of the cheap GFCI's made in china do not use the LM 1851 chip and thus do not have this delay.

You always know it is an inductive kick back problem because it will only happen when the inductive load is switched off, which I do not believe is the case in this thread as from the OP it sounds like it is a leakage problem, it could be as simple as the defrost pan heater element being bad and leaking to the case of the fridge?

Want to experiment with this to understand it better, go find a washer or another solenoid 120 volts and wire it to a switch, then get a cheap made in China GFCI receptacle from Menard's the cheapest ones they sell, and it should trip 40 to 60% of the time switch is turned off like a 1 in 6 ratio, it all depends on the timing of the current spike to the 60hz, I have done this using an O scope to demonstrate this problem.

What made me look at this closer was back before we had state wide codes we had a city that required all washers to be on a GFCI, the GFCI would always trip right after the fill solenoid shut off and the washer would be full of water, it was some condo's that had a small closet that a stack combo washer and drier would just barely fit and with the GFCI behind it was a pain to use a wet vac to drain the washer so it could be pulled out, we started using breaker type GFCI's and the problem went away so I wanted to know what was the difference and was why I found out that the LM 1951 chip had a delay that would over look inductive kick back types of trips.

 

[donaldelectrician]

thanx

thanx

This means i can make a tester with a Good GFCI !

Can we do similar with AFCI ?



Don

 

[GoldDigger]

Not always so, two current sources can be out of sync of different frequencies that can cause an imbalance it is not a problem of the current sources returning to is source as in Kirchoffs Law, it is a problem of what the current coil see's in a given instance of time, if we look at an inductive kick back on a circuit with a 60hz current on an O scope we can see that there is a spike of a very short duration that can be out of sync with the 60hz current, it can be an additive or subtractive to the 60 hz voltage for just a very short duration that because of the sync problem will put additive current when the 60hz is cresting on the positive side of the cycle but not on the negative side, the inductive kick back can have a much faster rise time and decay, it is of a higher frequency that can imbalance the circuit that can cause the current transformer in a GFCI to develop voltage,

We agree and yet we do not.

Unless you are talking about times on the order of one nanosecond, the time it takes light to travel about a foot, (corresponding to a frequency on the order of 1 GHz), there is no way that the currents can be unequal at two different points in a single closed loop circuit. The electrons have to be going somewhere.

What causes the effects that you observe with spikes, inductive kickbacks, and other transients is current through relatively small stray capacitances that make no noticeable difference at 60Hz but become important at higher frequencies. So when I am talking about reactive current paths, I am including ones in the range that you would not notice unless you were specifically looking at transients and high frequencies.

Let's now assume that the exact same current waveform was applied through both windings of the GFCI current sensor. If the coils are not necessarily identical in characteristics across that wide frequency range, you could then get a non-zero difference signal. One simple way for this to happen would be if one of the coils has a little more intra-winding capacitance than the other, so some of the current at high frequency is actually bypassing the coil instead of flowing through it.

That does not change the fact that the same current is flowing in both wires, it just means that the GFCI is not well enough engineered to behave well at that frequency. And, as you point out indirectly, it is easier to use a time delay to ignore those signals than to engineer them out, especially if part of the problem is capacitive couplings within the appliance. This delay takes care of both problems with one stone.

 

[kwired]

We agree and yet we do not.

Unless you are talking about times on the order of one nanosecond, the time it takes light to travel about a foot, (corresponding to a frequency on the order of 1 GHz), there is no way that the currents can be unequal at two different points in a single closed loop circuit. The electrons have to be going somewhere.

What causes the effects that you observe with spikes, inductive kickbacks, and other transients is current through relatively small stray capacitances that make no noticeable difference at 60Hz but become important at higher frequencies. So when I am talking about reactive current paths, I am including ones in the range that you would not notice unless you were specifically looking at transients and high frequencies.

Let's now assume that the exact same current waveform was applied through both windings of the GFCI current sensor. If the coils are not necessarily identical in characteristics across that wide frequency range, you could then get a non-zero difference signal. One simple way for this to happen would be if one of the coils has a little more intra-winding capacitance than the other, so some of the current at high frequency is actually bypassing the coil instead of flowing through it.

That does not change the fact that the same current is flowing in both wires, it just means that the GFCI is not well enough engineered to behave well at that frequency. And, as you point out indirectly, it is easier to use a time delay to ignore those signals than to engineer them out, especially if part of the problem is capacitive couplings within the appliance. This delay takes care of both problems with one stone.

Doesn't a GFCI just have one sensing coil? Both conductors, or all three for 120/240 circuits, pass through it, as long as current is balanced no net result appears to energize the coil and activate the sensing circuit.

 

[ELA]

I posted here that the GFCI can trip faster ( under nornal conditions) than some were/are stating as supposed fact.

http://forums.mikeholt.com/showthread.php?t=149465&page=2&p=1445387#post1445387

I posted here that GFCI's can trip even more immediately due to EMI. In many of these cases the differential sensing core may be completely bypassed.

http://forums.mikeholt.com/showthread.php?t=152331&page=3&p=1473338#post1473338

In this thread a differential current meter should be used to confirm that excessive leakage is, or is not, present.

 

[GoldDigger]

Doesn't a GFCI just have one sensing coil? Both conductors, or all three for 120/240 circuits, pass through it, as long as current is balanced no net result appears to energize the coil and activate the sensing circuit.

Point taken. Certainly the small sensor coil in an outlet-mounted GFCI works exactly as you state.
Larger imbalance detection systems at a source or breaker panel have other options, but they can also be built in exactly the same way.