2 GFCI Cause Issue?

[jim dungar]

080427-2055 EST

jim dungar:

For a voltage of a given amplitude as you increase the frequency the current thru a capacitor of fixed value will increase, Xc = 1/(2*Pi*f*C). Or for a fixed current amplitude as frequency is increased there is less opposition to current flow. Obviously a function of the load imedance the capacitor sees.

For a given average DC output current from a capacitor input filter the peak input current is much greater than the average ouput current, but short in duration. Maybe 10 times or more. Change to an inductive input filter so that current flows the entire cycle and the input RMS current is quite close to the average DC output current, and thus the peak input current is much lower and of a low frequency than for the capacitor input filter.

Beyond this are currents generated from the switching power supplies driving the motor.

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Line currents do not cause a GFCI to trip, only leakage current to ground is a concern So if filter capacitors are purposely connected to ground then a GFCI trip is justified..

And yes the frequency of the line currents will affect the coupling capacitance. But this is current on an unintended path and it should be interrupted.

 

[gar]

080428-0623 EST

jim dungar:

From the described symptoms my guess is that there is an input line filter and that the shunt bypass capacitors are tied to chassis and in-turn to ground providing the leakage path.

It would be interesting to know how much the ground leakage current is from this particular equipment.

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[DaveTap]

I'm curious if the cord mounted GFCI is actually working, too insensitive, or if the equipment would trip the garage GFCI if cord GFCI were removed (for testing purposes only)