| Repeating Rifle 2005-07-17, 4:25 am |
| I have some more information on what causes unusual tripping of my GFCI. I
have not had time to track it down because of other things to do. But, if
anyone REALLY understands what is happening, I will be interested in knowing
more.
I have been getting trips in my hobby greenhouse. I was using a switched
surge protector as a convenient way for on/off switching of a pump for
moving nutrient solution. To my surprise, the tripping takes place when the
pump is turned OFF.
I know that turning off a pump can provide an inductive spike if it gets
turned off when current is flowing in a winding. The transient, however,
cannot be fed back through the hot conductor that is already opened
already. I think that conduction through the neutral and ground wires is
required. But how can that happen?
The surge protector has filtering capacitance and varistors. Inductive kicks
can cause current to flow through them that otherwise would not be able to
trip GFIC. Capacitors also provide ground currents that may not cancelled by
opposite flow inside the current transformer used to detect faults. I know
that a 0.25µF from hot to ground will trip a GFIC. This operation is also
complicated by circuitry designed to detect neutral to ground faults.
I do have a switched power strip that contains no varistors or capacitors.
When I get a chance, I will find if I can obtain GFIC trips using turning
pumps with that. Meanwhile, there is an opportunity for someone to check out
and explain just what the tripping details are.
Bill
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