40 Volts on dishwasher frame, circuit board design issue?

[hbiss]

The condition you created by lifting the EGC is the abnormal condition that produced the 40V.

Yes. But it's indicative of a possible current flow when the ground is restored. The 40V could be a "phantom" due to the high impedance meter, maybe not. The only way to tell is to measure for any current.

-Hal

 

[tortuga]

The condition you created by lifting the EGC is the abnormal condition that produced the 40V. If the manufacturer uses capacitors for EMI filtering that can then create a voltage divider from Neu to Line w/respect to Gnd. When Gnd is lifted. If the Neu to gnd and line to gnd caps are exactly the same value you would read 60V.
The small value caps used are relatively high impedance so current flow is lower than the 5ma trip point under normal conditions.

Interesting,thanks my reptile brain thought that nothing in the appliance should be electrically connected to the EGC,
but I realize this is not the case.
I should not go off voltage measurements anymore and focus on measuring mA flowing on EGC.
I wonder why the 40 volts then and not 60 though?
And I if wonder if these filter devices can interact with each other?

 

[hbiss]

I wonder why the 40 volts then and not 60 though?

It would depend on the actual impedance of your meter. The voltage is really a useless number though, you are after the current value.

-Hal

 

[Mr. Serious]

I wonder why the 40 volts then and not 60 though?

Could be as simple as L-G capacitor and N-G capacitor have slightly different values, either on purpose or because of a wide tolerance band. Big filter capacitors sometimes have +80%/-20% tolerance.
Or there is other circuitry besides just two equal capacitors.
Or as Hal said, your meter is placing a load on the circuit and pulling the voltage down (and if that is the case, the dishwasher impedance to ground is high enough to be similar to your meter impedance, and the ground current would be much smaller than required to trip a GFI).

 

[Besoeker3]

I can't imagine a washing machine frame not being solidly connected to the earth wire (ground)) but that's here in UK.

 

[kwired]

Yes. But it's indicative of a possible current flow when the ground is restored. The 40V could be a "phantom" due to the high impedance meter, maybe not. The only way to tell is to measure for any current.

-Hal

Using a low impedance volt meter would produce enough current to drop that voltage if it is nothing more than "phantom voltage".

 

[kwired]

I can't imagine a washing machine frame not being solidly connected to the earth wire (ground)) but that's here in UK.

Your RCD devices are not set to trip at only ~5mA either.

 

[LarryFine]

Using a low impedance volt meter would produce enough current to drop that voltage if it is nothing more than "phantom voltage".

Agreed, or even trip the GFCI if it's "real" current. I use solenoid testers to test GFCIs.

 

[Besoeker3]

Your RCD devices are not set to trip at only ~5mA either.

Not sure what your point is?

 

[kwired]

Not sure what your point is?

Many these appliances we have here that don't play well with GFCI's probably won't trip a device that is set to trip at 30, 50 or 100 mA of fault current. Aren't your RCD's at least 30 mA or more?

 

[retirede]

I can't imagine a washing machine frame not being solidly connected to the earth wire (ground)) but that's here in UK.

That’s normal here as well. He only disconnected the ground wire to troubleshoot the RCD tripping issue.

 

[Besoeker3]

Many these appliances we have here that don't play well with GFCI's probably won't trip a device that is set to trip at 30, 50 or 100 mA of fault current. Aren't your RCD's at least 30 mA or more?

Nominally 30 mA but usually about 23 ish.

 

[synchro]

You liked this question, but didn't answer it:

Does it trip when plugged in, or only when turned on? If the former, I'd open the junction box and take a look.

Unfortunately I did not think to test that while I was there, I will when i go back.

I think doing what Larry said is important because if it trips when it's plugged in without it being turned on, then the tripping is being caused by a constant leakage current (and most likely from capacitors tied to the EGC for EMI reduction, as others have said).
But if it only trips when the appliance is turned on, then the tripping is likely caused by a VFD or other switching electronic devices within the unit as Hal mentioned.
Of course, capacitors could be contributing some leakage current even if it's not enough to cause the GFCI to trip by itself.

If the GFCI trips without the unit being turned on, then I think the following test could help confirm the root cause of the leakage, as long as there's time available to do such a test:
Assume that a capacitance of x μF inside the appliance is causing a leakage current I_L to flow from the GFCI's load side hot terminal to the EGC. Then if a capacitor with the value x μF is connected between the GFCI line input hot terminal and the load side neutral terminal, then a current I_L will flow back into the load side neutral terminal. This current flowing back will then cancel the magnetic field within the CT of the GFCI that's being caused by the appliance leakage current I_L. Therefore, if the appliance is plugged in then the GFCI should be able to be reset due to this opposing current flow. An 0.1 μF capacitor would draw about 4.5 mA with 120V across it, so that could be a starting point and then varied if desired.

This would only be a test to confirm that a capacitive current of a known amount is causing the tripping. It would definitely not be an acceptable fix for a problem inside of the appliance, because it's effectively biasing the trigger region of the GFCI off from 0 mA.
I realize that digging this deep into the problem may not be ultimately necessary to bring closure to the OP's situation, but I think it could at least provide an opportunity to get some insight into what's going on.