Ned,
I would strongly advise you to test for actual trip current rather than
relying on the "test" button. I would use a > 2 watt potentiometer (20K) and
slowly reduce the resistance until each GFCI trips while monitoring the
milliamps with a multimeter. The "test" button is a coarse test only. The
heart of a GFCI is a small IC (from National I think) which monitors the
output of a pickup coil around a ground conductor. When an overcurrent is
detected the IC actuates a small solenoid that triggers a spring-loaded
disconnect. While very robust, the IC can be damaged by high voltage
transients. I found this out several years ago while helping develop a high
voltage gate circuit for a time-of-flight Mass Spec. system. We damaged the
GFCI outlets on the workbench due to capacitive coupling back into the line
(pulse transformer to DC-DC module to power supply). We suffered several
nuisance trips before fatally damaging the GFCI outlets.
My point is this: If the circuits tripped because you got a temporary
increase in ground leakage of appliances plugged into the GFCI, they are
probably OK. If, however, the IC inside of the GFCI was exposed to a surge,
it probably suffered SOME damage and might fail at a later date. I would
replace all of the GFCI outlets which tripped, since there is no way to
determine what actually happened.
Scott Lacey
-----Original Message-----
From: Ned Devine [SMTP:[email protected]]
Sent: Tuesday, July 20, 1999 10:34 AM
To: 'IEEE, EMC/Product Safety'
Subject: Lightning and GFCI
Hello,
Recently my house got struck by lightning. One of the things that
happened
was that all of the GFCI's tripped. I reset them and tested them
(pushed
the little test button) and they seem to work.
My neighbor stated that when their old house got struck by lightning
all of
the GFCI's were damaged. They did not find out till they went to
sell it 3
years later and it failed the electrical inspection. Now, she is a
software
engineer, so I am taking her comments with a grain of salt :-),
but....
Does anyone know if lightning could damage the GFCI's so that they
would
test OK but still not work? If I want to test the GFCI's, could I
just hook
a 15 k ohm, 5 Watt resistor from line and neutral to ground? Has
this
happened to anyone else?
Ned Devine
Entela, Inc.
Program Manager III
Phone 616 248 9671
Fax 616 574 9752
e-mail [email protected]
PS The EMC testing you do is working. Most of the new
electronics
survived. The only newer items that died were the garage door
opener and
the cordless answering machine.
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