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    Leviton GFCI nuisance tripping and circuit analysis

    I know many electricians and vendors, engineers encounter nuisance tripping with the Leviton GFCI. After all these years. Is there finally a theory why? If not. Let's figure it out and analyze the circuit.

    First. This is a Waterpik mouth spray shaded-pole motor. See youtube video how it works at

    https://www.youtube.com/watch?v=PmNcRsxSovs




    Even if the plug is 2-prong (without any grounding and it's put on glass surface). The Waterpik motor can consistently trip the Fairchild chipset (I tested 4 units and same results). This is used in the Leviton. It doesn't trip on other brands of GFCI such as the Siemens GFCI. It's even when the motor was isolated and not wet (even if rotor removed). The trips occur either during startup or turning off (50% of the time). Not when it's already on.

    For other load that trips sometimes, it's difficult to figure it out. But not this when it can do it consistently so we can do experiments that can figure out the technical reasons.

    This is the circuit diagram of the GFCI also used by Leviton.




    http://datasheet.elcodis.com/pdf2/81...29/rv4141a.pdf

    See the Leviton teardown at https://www.powerelectronictips.com/...t-interrupter/

    The second sense coil works only if there is a ground, right? So what part do you think is tripping the circuit? There are many theories elsewhere. Some say the inductive load could have the magnetic field still not going to zero in one wire producing temporary imbalance in the sense coil, but why doesn't it trip other brands of GFCIs (such as the Siemens)?

    https://www.justanswer.com/electrica...hen-clear.html

    Why is your theory? Don't suggest wiring problem because it is not that.

    This is important for electricians, vendors, engineers and even users to know the reasons so can share the knowledge and avoid headaches and inconvenience.

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    190106-2516 EST

    tersh:

    I have expressed an opinion on this before.

    Look at the board layout. There is a long trace from where C3 is located to the SCR gate. I suspect that transient capacitive coupling to the SCR gate is the cause.

    Try putting C3 directly at the SCR gate, and a 100 ohm carbon comp resistor in place of the trace. This creates a low pass filter at the gate input and also reduces the capacitive coupling to the gate.

    I think that inductive kick at either turn on or off is the source of the transient.

    .

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    Quote Originally Posted by gar View Post
    190106-2516 EST

    tersh:

    I have expressed an opinion on this before.

    Look at the board layout. There is a long trace from where C3 is located to the SCR gate. I suspect that transient capacitive coupling to the SCR gate is the cause.

    Try putting C3 directly at the SCR gate, and a 100 ohm carbon comp resistor in place of the trace. This creates a low pass filter at the gate input and also reduces the capacitive coupling to the gate.

    I think that inductive kick at either turn on or off is the source of the transient.

    .

    But even if the motor is 3 meters away from the GFCI outlet. It still triggers it. What is the range of the capacitve coupling. Maybe by using long extension, one can test if capacitive coupling is the cause?

    Do you find it present in all Leviton models (with and without the 2015 auto-monitoring self-test?) Why don't other brands have the same issue?

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    Quote Originally Posted by tersh View Post
    So what part do you think is tripping the circuit?
    If you mean the grounded-neutral: Bypassing RG is the only thing I can see.

    If you mean the nuisance tripping: I'm guessing the appliance switch arcing.

    I have no idea why it's sensing arcing, though.
    Last edited by LarryFine; 01-07-19 at 03:49 AM.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    I don't generally use Leviton GFCI's so don't know how prone they are to such trips.

    I do agree that it is likely inductive kickback that is causing the problem if you know there is no ground faults going on, probably happens either when turning on or turning off the appliance?
    I live for today, I'm just a day behind.

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    190107-1719 EST

    tersh:

    I am talking about capacitive coupling within the GFCI device. Thus, the length of wire from the GFCI to the load is not a big factor other than how that affects the voltage transient level when it gets to the GFCI device. The suggestion I was making relative to the GFCI circuit board is to put the shunt capacitor directly at the gate-cathode of the SCR instead of about 1" away. And the series resistor ln combination with the shunt capacitor to the gate is to reduce transient voltage at the gate.

    .

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    Quote Originally Posted by gar View Post
    190107-1719 EST

    tersh:

    I am talking about capacitive coupling within the GFCI device. Thus, the length of wire from the GFCI to the load is not a big factor other than how that affects the voltage transient level when it gets to the GFCI device. The suggestion I was making relative to the GFCI circuit board is to put the shunt capacitor directly at the gate-cathode of the SCR instead of about 1" away. And the series resistor ln combination with the shunt capacitor to the gate is to reduce transient voltage at the gate.

    .
    Have you tried doing it to a Leviton GFCI circuit board itself? Why didn't you?

    Also why is only certain motors affected, like shaded-pole motor in Waterpik but not washing machine motors?

    Does a refrigerator have any motor that can do that? When I used the Fairchild based GFCI similar to Leviton, my refrigerator trips the GFCI once or twice a day. But not the Siemens GFCI (which I'm still testing and it's been a day without trip already). If the fridge won't trip the Siemens GFCI for more days then it solves a mystery why seemingly new fridge can trip GFCIs. It's not the fridge fault but the GFCIs.
    Debate rages whether the inductor in fridge can lose the current. Since it doesn't, many suggest to replace the fridge. I didn't read any suggestion it is the GFCI fault.

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    As far as issues with refrigerators,

    The circulation fan in the freezer section behind the back panel is a shaded pole just like the ones used in exhaust fans. So one could expect the same results at turn on and shut off. Unless the problem had anything to do with defrost element issues or erratic compressor issues.

    My experience with the Leviton GFCI receptacle was primarily when the shaded pole motor was shut off. Because often times a customer would leave the bathroom, turn fan off, and upon returning the GFCI would be in the tripped position.

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    Quote Originally Posted by gar View Post
    190107-1719 EST

    tersh:

    I am talking about capacitive coupling within the GFCI device. Thus, the length of wire from the GFCI to the load is not a big factor other than how that affects the voltage transient level when it gets to the GFCI device. The suggestion I was making relative to the GFCI circuit board is to put the shunt capacitor directly at the gate-cathode of the SCR instead of about 1" away. And the series resistor ln combination with the shunt capacitor to the gate is to reduce transient voltage at the gate.

    .
    Something important to share. In the original Leviton circuit, did you see the distance between SCR and C3 an inch? In the china gfci, the distance between SCR and C3 is only mere 1/4 inch. Here:



    The whole circuit is only about 2.25 inches long:



    This was the reason they couldn't fit a mechanical reset because it needed many spacing.

    Anyway. The US Leviton is much larger. So maybe someone can test on the actual Leviton because there is possibility the inductive kick in both may be via different mechanisms. Your theory may be correct for the actual Leviton. But please share something in the following before I move on from this. .

    In the original Leviton circuit using this bare diagram which I have almost memorized:



    1. How come if the SCR is 1" away from C3. It can more likely produce capacitive coupling? Also I think you are saying the capacitive coupling source is the red path above, right? And it getting into the gate? but why does long distance make capacitive coupling more likely? This is to understand other circuits too and not just it.

    2. If you short the gate and cathode of the SCR, how much the false trigger disappears? When you short the cathode to the gate, is it not like the gate is triggered?

    3. My thesis in college engineering was ultrasonic cleaning machine. I could have focused on GFCI back then. Whatever, it would be easy to put the solenoid back or other load to test whether the shaded pole motor inductive kick can trigger it without the chip. I'll let you know. I spent 5 years in college and it would be crazy if I couldn't even do this. But I generally avoid electronics because the cell or neurons in biology is way advanced than any electronics.

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    190115-0811 EST

    tersh:

    Your 1 --- Take two straight wires of of some fixed dimensions and spaced a fixed distance apart, then the capacitance between the wires is proportional to length. Longer length more capacitance. Also as the length of a wire increases so does its inductance.

    Your red line is in the wrong place. There is already resistive continuity for that path. The red line needs to end on the gate, and start at the upper power line wire.


    Your 2 --- When the gate is shorted to the cathode it is very difficult to get a trigger voltage to the gate.


    Your top picture --- The C3 is in a very good location. In the Leviton I looked at there was a much longer trace.

    In the present circuit with no IC installed, but otherwise all the circuit for the gate is unaltered, is there any false triggering?

    If you started with a new circuit and removed the 1N4004 diode that feeds pin 5, labeled "line", this removes power to the IC, then would false triggering occur. If false triggering was eliminated, then this would tend to indicate that SCR triggering was coming from the IC. It is possible you could remove the 1N4004 to perform the test, and then reinstall it so this might not be costly.

    .
    Last edited by gar; 01-15-19 at 09:53 AM.

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