system goes back to normal.
So, how do I know it opened at five milliamps? Also,
the number of times the GFCI is opened ... doesn't that
potentially damage the breaker? If I test it monthly, how
often do you recommend changing them out? If there is a
way to do this, what equipment do I need? A regular
amp/voltage meter? Thanks and best regards.
— William (Bill) Griffin
SSHO Phase III
AGFCI — which stands for Ground Fault Circuit Interrupter — is a device which monitors the flow of current in the "hot" and "neutral" electrical wires in order to sense a ground fault
in which the currents in these two wires are not equal (as
is the normal case). If the GFCI senses a four to five
milliamps (mA) current imbalance, the circuit is broken
within 33. 3 milliseconds to protect the human.
The ground fault normally encountered is the current
running through another conductor (such as the human
body) which we try to prevent. Roughly 30 mA of AC or
100 mA of DC current will cause the heart to fibrillate
which causes death.
Electricians should ALWAYS work in pairs and know
CPR. (Kudos to the power company line technicians who
work on energized high voltage lines.)
The GFCI is basically a fast circuit breaker which
senses a potential electrocution, so breaks the current to
protect human life. GCFIs come in a wide variety, from
the receptacle with the "RESET" and "TEST" buttons found
in restrooms, to the industrial devices on lines carrying
hundreds of amps.
The Residual Current Detector (RCD) is the same
thing as a GCFI. [Aside: Years ago, I heard a story of an
engineer who specified GFCI breakers on lighting circuits
that fed a fluorescent lighting bank. The way fluorescent
operated on start-up tripped the GFCIs so these breakers
had to be replaced. Expensive lesson!!!].
GFCIs are used in residences in bathrooms, kitchens,
swimming pools, hot tubs, spas, etc., where humans,
electricity, and water are close together. Your concerns
about whether or not the GFCI trips at the proper 5 mA is
akin to the old problem of whether or not the light in the
fridge goes off when you close the door, but involves
Residential "fixed" GFCIs should be tested monthly
by ensuring that the test button "pops" the GFCI
10 January 2015