Update: I consulted with other electrical engineers. Here is a plausible mechanism. Again refer to the circuit diagram of this GFCI:

GFCI schematic

Look at the board layout. There is a long trace from where C3 is located to the SCR gate. It is suspected that transient capacitive coupling (within the circuit and not from outside) to the SCR gate is the cause.

Suggestion is to 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.

The inductive kick at either turn on or off may be the source of the transient.

The series resistor in combination with the shunt capacitor to the gate is to reduce transient voltage at the gate.


Original message:

Does anyone own any Leviton GFCIs (those models without any automatic monitoring self test)? I found out the shaded pole motors from Waterpik can constantly trip on them (50% of the time), but not other brands of GFCI (which I just tried). Someone in the following url has similar experiences with his Leviton GFCI and even a second new Leviton he bought.


So it may not be problems with the normal working of a GFCI but particular implementation of the Leviton GFCI. Anyone got a clue what is that mechanism that can cause shaded pole motors to trip on the Leviton GFCI?

The youtube video describes the shaded pole motor in the Waterpik in details. https://www.youtube.com/watch?v=PmNcRsxSovs

To recap. Even if the plug is 2-prong (without any grounding and it's put on glass surface). The Waterpik motor can trip any Leviton 5mA GFCI (I tested 4 Leviton GFCI outlets) even when isolated and not wet (even if rotor removed). The trips occur either during startup or turning off. Not when it's already on.


In other motor/GFCI combination. What is the reasons why it could trip during startup or turning off. It's not wiring problem. There are many reports of this everywhere. Have you experienced or read about it? What is the mechanism for the constant tripping? (supposed it's not wiring problem which I'm sure it is not in the waterpik motor and Leviton?

You may have heard of new refrigerators tripping on new GFCI. It could if the GFCI is a Leviton brand.. which may not be compatible with refrigerators. I have new refrigerator that also trips every few hours on the Leviton GFCIs. I'm testing it with other GFCI now. Please share your experiences about this too.

Btw, I use GFCI on all my electronic projects to be on the safe side.

  • 1
    \$\begingroup\$ What you have here appears to be a shaded-pole motor. No idea on the GFCI issue so I'll let someone else answer that. \$\endgroup\$ – duskwuff Jan 6 at 11:05

So do all shaded pole motors trip on any GFCI?

No. There is nothing in the design of a shaded-pole motor or any other type of AC motor that makes them particularly vulnerable to tripping a GFCI. There are electronic speed controllers (ESC) that can create a vulnerability, but that is not relevant to your situation.

Does anyone know what kind of rotor/stator is the following?

You have already determined that it is a shaded-pole motor. That is correct and the YouTube video that you linked is mostly correct The rotor is usually described as steel with aluminum bars rather than aluminum with steel bars. That particular style is often called a C-frame shaded-pole motor.

Since there is no way for the current to be lost to ground. What could be other mechanisms?

I would suspect a problem with the GFCI or wiring. Check the Waterpik in other GFCI outlets and other loads in the outlet in question.

Could it be inductor at one wire taking time to go to zero so it creates temporary imbalance? Is this an accepted explanation?

I don't think so. There may be some problem with the wiring that causes a GFCI problem when something is switched on. That would be worth researching.

What kinds of particular motor types can trip GFCI akin to the above?

There are none except for the ESC mentioned above.

  • \$\begingroup\$ It's not wiring problem because it's only 2 prong. Do you have a theory what part of the GFCI can trip easily on some motors? What particular issue can cause it (in other cases you have encountered or heard)? \$\endgroup\$ – Jtl Jan 7 at 2:09
  • \$\begingroup\$ I don't believe that there is a nuisance GFCI trip problem with any type of motor not connected through an ESC. The problem that I suspect is not in what is plugged into the GFCI but in the GFCI itself, wiring to other outlets connected to the GFCI, or other wiring in the house. \$\endgroup\$ – Charles Cowie Jan 7 at 3:35
  • \$\begingroup\$ So what part inside the GFCI can malfunction when motor is switched on or off? any guess? is inductive load having delayed magnetic field becoming zero hence causing temporary sense coil imbalance not a problem, why? \$\endgroup\$ – Jtl Jan 7 at 3:38
  • \$\begingroup\$ I would not try to determine what might be wrong with the GFCI. If you suspect it may be bad, replace it. First "Check the Waterpik in other GFCI outlets and other loads in the outlet in question." as I mentioned above. GFCI outlets work with inductive loads all the time with no problems. Any effect of a load on the current vs voltage will be the same for the whole circuit not one conductor vs the other. \$\endgroup\$ – Charles Cowie Jan 7 at 4:05
  • \$\begingroup\$ Keep in mind that refrigerators are more likely to be grounded and may have capacitive paths to ground due to transient protection etc. I would view the Waterpik as being less likely than other products to be a problem for a GFCI with a marginal design. This is a rather interesting problem and a distraction from my sciatica pain, but I can not do the research needed. \$\endgroup\$ – Charles Cowie Jan 8 at 14:26

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