Date: Fri, 10 May 2002 13:00:26 -0700

Author: Earl Dolnick

Subject: Re: GFCIs

Post:

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HI Tappers:=0D=0A Gfi's are fairly simple devices. A simple iron =
core transformer has a 2 winding primary. One winding is in series wi=
th the hot lead and the other winding, wired in reverse, is in series=
with the neutral return. If all the current in the hot winding match=
es the current in the neutral winding, the fields cancel. If they don=
't, it is assumed that some of the current flowed to ground via anoth=
er path. The unbalance causes a current to flow in the secondary of t=
he transformer, which is detected and turns on a triac wired directly=
across the power line.That causes the conventional breaker to blow o=
pen. Sensitivity was about 10 ma unbalance. It may be better today, b=
ut any greater sensitivity could cause false triggering=0D=0A =
Many years ago, I installed a GFI in the bathroom and outdoor circu=
its. I would test it periodically, and the first one failed. So did t=
he second one. The 3rd sees to be ok. The circuit is simple, but it d=
oes depend upon some circuitry that is connected to the power line, a=
nd subjected to assorted transients. It's ok to use as long as it is =
tested regularly, but watch out. It's risky to trust your life on a f=
ew chips and a big SCR.=0D=0A=0D=0A Cheers, Earl D.=0D=0A=

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=0D=
=0A=0D=0A html; charset=3Diso-8859-1">=0D=0A 00" name=3DGENERATOR>=0D=0A=0D=0A=0D=0A Color=3D#ffffff>=0D=0A

HI Tappers: ONT>
=0D=0A
    G=
fi's are fairly  simple =0D=0Adevices. A simple iron core transf=
ormer has a 2 winding primary. One winding is =0D=0Ain series with th=
e hot lead and the other winding, wired in reverse, is in =0D=
=0Aseries with the neutral return. If all the current in the hot wind=
ing matches =0D=0Athe current in the neutral winding, the fields canc=
el. If they don't, it is =0D=0Aassumed that some of the current flowe=
d to ground via another path. The =0D=0Aunbalance causes a current to=
flow in the secondary of the transformer, which is =0D=0Adetected an=
d turns on a triac wired directly across the power line.
=0D=0Aface=3DArial size=3D2>That causes the conventional breaker to b=
low open. Sensitivity =0D=0Awas about 10 ma unbalance. It may be bett=
er today, but any greater sensitivity =0D=0Acould cause false trigger=
ing
=0D=0A
PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; =
MARGIN-RIGHT: 0px">=0D=0A
 &nb=
sp;      Many years =0D=0A ago, I installed a GF=
I in the bathroom and outdoor circuits. I would test it =0D=0A perio=
dically, and the first one failed. So did the second one. The 3rd see=
s to =0D=0A be ok. The circuit is simple, but it does depend upon so=
me circuitry that is =0D=0A connected to the power line, and subject=
ed to assorted transients. It's ok to =0D=0A use as long as it is te=
sted regularly, but watch out. It's risky to trust your =0D=0A life =
on a few chips and a big SCR.
=0D=0A
=3DArial size=3D2> 
=0D=0A
size=3D2>Cheers,  Earl =0D=0AD.
=
=0D=0A=

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