Date: Fri, 10 May 2002 09:17:02 -0400

Author: James Frysinger

Subject: Re: GFCIs


You have got to be pulling our legs! I've heard of some safety-defying demos,
but this one takes the cake!

Perhaps there's some misconception about GFIs. Those letters stand for
"ground fault interrupter". The purpose is to detect an (unwanted and
potentially lethal) fault to ground and to interrupt it quickly. The device
is NOT designed to protect against short circuits; the normal circuit breaker
or fuse is there for that purpose. If ONE side of the circuit (the "hot"
side, that is) were to be faulted to ground, possibly via a human being, then
the GFI would trip the circuit due to the extra current flowing in that leg.
Of course, in an ideal circuit, the "cold" side could be faulted to ground
with no problem. Indeed, the electric code is designed to try to keep that
side of the circuit at ground potential -- hence the requirement for
polarized plugs (wide and narrow blades). It is the imbalance of currents in
the "hot" and "cold" legs that causes the trip to occur.


On Friday, 2002 May 10 0829, you wrote:
> I saw a demo once where bare wires were used to light a bulb then the wires
> were touched to the presentor's tongue. I have thought about it but never
> tried it. One of these days there may be a defective unit :)
> ----- Original Message -----
> From: "George M. Caplan"
> To:
> Sent: Friday, May 10, 2002 7:25 AM
> Subject: GFCIs
> > I am thinking of creating a demo or experiment involving Ground Fault
> > Circuit Interrupters.
> > Have any of you done this already?
> > Anyone know whether GFCIs will work at low voltages e.g. 12 VAC?