I have been using GFCI extension chord for over 7 months. It is
a 50 foot cord and has never tripped. I bought it on my last visit to
Japan in January 1998. The Japanese incorporate GFCI in all outdoor
extension chords. Several times the cord was wet when I put it away.
I tested it with a resistor to ground and it does trip at 4.2ma.


Oftentimes, natural leakage thru the insulation of a long extension cord
(read 50-100+ feet) or from a long inside-the-wall run to another outlet
is enough to trip a GFCI (Ground Fault Circuit Interrupter). A GFCI
works by "sensing" the current running thru the hot and neutral lines
and comparing them. If the difference between the two is >5 ma
(milliamp=1/1000 of an amp), GFCI's are supposed to trip. For example,
if you are vacuuuming the car, there might be, say, 5 amps going down
the hot line and 5 amps coming back up the neutral (I know, not exact,
but for brevity's sake). This is normal. Say you step in a puddle
while turning the vac off. Now, 5 amps might be running thru the hot
line, but since you offer less resistance to the current than the
vacuum's motor, that current is going to pass thru you into ground
instead of going back up the neutral line of the cord. The current thru
both wires is not equal now. The GFCI trips, hopefully in such a quick
time that the 5 amps runs thru you for a *very* tiny moment. The real
problem arises when there is a long run between the line (the GFCI) and
the load (telescope, light, weedeater, vacuum). Insulation isn't
absolutely insulative (is that a word?). There is always a small
leakage from the hot line to ground (the actual "ground" wire, the outer
insulation, the ground itself, whatever.) On a long run, this leakage
can accumulate to a large enough amount to cause a properly working GFCI
to trip needlessly. I have seen this happen many times. I have even
seen a GFCI trip with 250' of extension cord plugged in and nothing
else.

Mike

I am not an electrician...however, is seems nobody has told the rest of
my family.


James W. Burrows wrote:
>


Chris Frye
Silver Spring, MD.

View index by [date] [author] [subject]
Previous message: Re: [M]: OT Observatory, Andy Wallace
Next message: Re: [M]: Reticle EP recommendations, Michael J. Cook
Next message in thread: Re: [M]: Powering the LX200, Len Gordon
Previous message in thread: Re: [M]: Powering the LX200, Andy Wallace