On Dec 30, 9:02*pm, BobK207 wrote:
On Dec 30, 10:12 am, M Q wrote:





T. Rex wrote:
In article ,
says...

Doug Miller wrote:

In article , HerHusband wrote:

Whether resistive or inductive, how can you have current flow unless the
circuit is completed?

Back-EMF can flow through the neutral wire because the neutral is connected to
ground at the breaker box.

Open the hot wire and current shouldn't flow through
the neutral either, unless there really was a fault in the wiring
somewhere?

Back-EMF from the collapsing magnetic field in the motor windings when it's
switched off.

You basically have a 2 wire inductor. You are saying that when the
circuit is broken, magnetic field collapse produces a current flow in
one wire that is not equal to the current flow in the other wire. You
may be in line for a Nobel Prize. Or maybe not.

Pay attention this time. The currents _at_the_GFCI_ are unequal, because
one of the two wires is not connected to the GFCI.

I think that YOU need to pay attention:
In the wire that is not connected we can agree that the current is zero?
In the wire that is connected, what do you think the current is?
If it is zero, they are equal and the GFCI should not trip.
If it is not zero, where do you think that current is going?
Those electrons have to go (come from) somewhere. *They are not
getting stored in the fan. *They could be going to ground, but
only if you have a ground fault.

MQ-

Sorry for the potentially redundant post but......

Since the GFI is tripping we know that somehow the currents compared
by the GFI's circuit are different; the hot is zero since the switch
is open, thus the current at on the neutral is non-zero.

If it is not zero, where do you think that current is going?

It's going from the fan collapsing field thru the neutral wire back to
the neutral / ground bus at the service panel.

Those electrons have to go (come from) somewhere. *
They are not getting stored in the fan.

Actually, they're kinda stored "stored in the fan"......in the
magnetic field, while the fan is running.

They could be going to ground, but only if you have a ground fault.

They are going to ground, but not thru a fault....but thru the neutral
wire.

MQ, this is just my understanding of how motors & GFI can
interact......... I could be wrong but I believe this is a reasonable
theory.

cheers
Bob- Hide quoted text -

- Show quoted text -

Any current produced in this way will be way too small to trip the
GFCI. The capacitance to ground of the now open hot wire bewteen the
motor and the switch is way too small to support the required current.
If this theory was correct then the GFCI could be made to trip by
applying line voltage across the motor from a separate branch circuit,
one on the same leg, while the switch is open. Back emf is voltage,
not current.

Though I applaud the effort.

How about static discharge from their finger to the switch when they
go to turn it off?