DIYbanter - View Single Post - I thought the GFI was supposed to trip ?????

Pop`

wrote:
CJT wrote:
Warren Block wrote:

wrote:

I just went to an auction and came home with a whole bunch of old
junk. One of them was an old metal framed swivel house fan. I am
always leary of that old stuff, so I always test it in a GFI
outlet.

I plugged it in, and reached to flip the metal switch. When I
touched it, I got a fairly good jolt on my fingers. The GFI did
NOT trip. WHY? I thought that was the whole purpose of having
them.
This GFI was just purchased and installed, and the test button
works fine.

Two-prong plug on the fan, right?

Irrelevant.

The amount of current on the hot line is the same as that on the
neutral. So as far as the GFI is concerned, there's no ground
fault. It can't tell if it's just the fan motor between hot and
neutral, or the fan motor and you.

The current through his body returns to ground (just like the garage
floor test that follows), not neutral.

Certainly seems that the current through the GFCI should be
unbalanced. The only way it would be possibile for it to be equal
would be if
you grabbed one part of the fan that was shorted to hot, and another
that was connected to neutral.

No. I understand why you think that way, but it's not so. The current on
each line under ideal conditions will be exactly equal. Current is not
"lost" inside the fan motor. It's too much to go into here, but here's a
link might help you get started:
http://www.reliance.com/mtr/mtrthrmn.htm

Pop`

Just for the heck of it, I plugged the fan in again, and had the
switch already turned on. The fan ran just fine on a wooden table.
Then I set it on the cement garage floor and plugged it in again,
and the GFI tripped instantly. For the heck of it, I put a piece
of wood under it (on the floor) and the GFI did not trip. This
proves that fan motor has leakage to the metal housing, so it goes
in the garbage. But I can not understand why the GFI did not trip
when my fingers got shocked ????

The cement floor provided a current path to ground, so the amount of
current on the neutral was different from what was on the hot. The
GFI sees that difference and trips.

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