Ground Fault Circuit Interupter (a.k.a. GFI or GFCI)
Installation, Troubleshooting and Uses
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My question is on GFCI outlets. I have a three prong outlet in my
bathroom, but it is a phony since my electrical wiring is very old and
there is no safety grounding -- the third prong does not connect to
anything. I tried to use a portable GFCI. The portable GFCI has three
prongs where it plugs into my receptacle so does this mean that my
receptacle must be grounded, in which case I can't use the portable
GFCI? I read your article on GFCI and I am still confused because your
article said that the portable GFCI must be connected to a grounded
circuit but a regular GFCI outlet can be installed without a ground.
I did plug the portable GFCI into my ungrounded outlet, but the
portable GFCI started making a humming noise. What is this noise?
MG from NY, NY
Sorry about the confusion. I went and reread the passage, and I
became confused too. My head was turning two ways at once, and the words
Because portable GFCIs are generally used in hazardous
situations... most are used by contractors and tradespeople on work sites... they should
be used in grounded situations. Since GFCIs can and do fail, using a metal framed portable saw in the grass and compounding the
danger by not providing a ground for the tool is dangerous!
However, portable GFCIs do not need a ground to function, since
they are designed the same as stationary ones. In fact, one
reason for using a GFCI is to protect a person in case the ground is
Remember that GFCIs protect from extreme shock, but slight shocks
can occur before the GFCI disconnects the power! Therefore
people who might be adversely affected by very slight shocks (people
with critical livesaving devices such as pacemakers, for example)
should be even more cautious!
I am unsure what the humming noise is, but it can only be a
malfunction, even if the unit appears to be working OK. Best to err on the side of
caution with electricity. Even though the cause of the noise is
unknown, I would suggest replacing the GFCI.
Thanks a lot for allowing me to clarify my remarks.
In regards to GFCI outlets, how do I choose the one with the proper
amperage? I noticed that there are different types.
JD from Victoria, TX
GFCI's (ground fault circuit interrupters) are electrical outlets that have a
protective circuit built into them to help prevent life threatening electrical
shocks. (We have an article on GFCI... click
The easiest way to determine the correct amperage is to select a GFCI with
the same amperage as the circuit breaker for that outlet.
The other way is to get a wire gauge checker at the hardware store and
determine the size of the wires in the circuit. Turn off the power first, of
course! Generally, 15 amp circuits use 14 gauge or larger wire and 20 amp
circuits use 12 gauge or large wire. The smaller the gauge, the larger the wire.
I have noticed over the years that many hardware stores only stock 15 amp
GFCI's, so you may need to go to an electrical supply house or home store to get
the proper sizing for 20 amp appliance circuits.
Please help me. I am a single woman with a problem! I recently let
out my basement to boarders and they lost power in the outlets
they had their television and stereo plugged into and also in the
back room where their refrigerator is. These outlets just don't
work! I checked all the fuses and they are fine. I tried shutting
off the main power and turning it back on again but this did
nothing... except I had to reset all the clocks! I don't know what
else to do!
As you describe the problem, I can see three possibilities. The
first is that there is a second "fuse" or circuit
breaker box in the basement that you are missing which controls
the affected rooms. Sometimes when doing renovations, secondary
boxes are added to allow for more electrical circuits rather than
replacing the main board. Take a good look around if you are
The second is that a wire has come loose SOMEWHERE. Since this
power loss affects so many outlets it would have to be a wire in
either the main panel (a.k.a. "fuse" box) or in another
electrical box that acts as a feeder for all these outlets. Repair
would require you to turn off the power and manually inspect every
likely electrical box for a disconnected wire and properly
reconnect it. If you don't have any electrical savvy, though, this
could be very dangerous and ill advised! Making the wrong
connection could be more than just shocking... it could be deadly.
Getting an electrician would be a wise idea.
The other possibility is that the circuit is protected by a
ground fault circuit interrupter (a.k.a. GFCI). These nifty
devices act as a first line of defense against electrical shock
and are normally installed to protect outlets and fixtures in damp
locations such as outdoors, garages, near kitchen and bathroom
sinks, etc. It is not uncommon for them to be installed in
basements or in mixed circuits that include bathrooms.
There are two types of GFCI's. One type takes the place of a
wall outlet and has "reset" and "test"
switches clearly visible on its face. One of these outlet-type
GFCI's can protect a number of other outlets if wired correctly. If
one is tripped, the power is restored to the circuit by simply
pressing on the "reset" switch until it clicks.
The other type of GFCI is a special circuit breaker in your main
panel. The face of the circuit breaker would have a white or
colored button labeled "test". To reset it, you must
flip it completely off and then back on.
I know you said you checked the "fuses", but I
remember that my folks always called the circuit breaker box a
"fuse box". Old habits die hard, so just in case you
really meant circuit breakers I have included this info (and for
all our other readers, too!)
It is possible that your boarders used an appliance such as a
hair dryer or a vacuum cleaner that caused the GFCI to mistakenly
think an electrical short or "ground fault" had
occurred, shutting down the circuit. They should be told about the
GFCI so that they can reset it themselves if this happens again. A
GFCI that begins to trip frequently may need to be replaced.
I have an article at the website on GFCI's at the following URL:
You are misleading in stating that a grounding wire is needed
for GFCI (ground fault circuit interrupter) protected outlets!
Shame on you! The added cost of adding a grounding wire will stop
most people from adding GFCI units.
And you are wrong in that a GFCI without a grounding wire will
a person using a 3-wire tool! Please get your facts straight!
CM from Huntsville, AL
Respectfully, maybe you are misreading what I said. This is a
confusing issue and there is quite a bit of "heat" on
each side of it.
If you read my article on GFCIs, I make it very clear that a
ground is NOT needed for a GFCI to function properly. However, do
you disagree that certain tools and appliances have a third
grounding plug for a good reason? Are the manufacturer's crazy...
or is there a reason, perhaps related to safety?? Of course there
is... it is because these appliances do not meet the UL
(Underwriters Laboratory) standards of "double
insulation", thus posing a potential shock hazard when the
appliance is touched under certain conditions.
Grounding is required in all new electrical work... but there
is an "exception" for GFCIs used in "old",
ungrounded wiring. As you imply, it is better to have a GFCI in a
bathroom than NOT have one... I couldn't agree more.
Obviously cognizant of the potential hazard of using
three-pronged appliances in ungrounded circuits, though, the NEC
(Nation Electrical Code) requires that ungrounded GFCIs must be
identified with a label as "ungrounded". In other words,
ignore the warning at your peril. Like the labels on cigarette
GFCIs are designed to prevent electrocution, NOT electric
shock. In my reading on this subject, there seems to be quite a
bit of rancor on whether or not the NEC should allow this
grounding exception for GFCIs. It has been demonstrated that the
amount of shock a person receives before the GFCI activates can be
enough to cause injury or death related to the uncontrollable
muscular reaction that can occur. OSHA (Occupational Safety and
Health Administration) has also issued directives concerning the
use of GFCIs in place of proper grounding in a nursing home that
did not have proper grounding.
OSHA, in my opinion, has this one right... it only takes a
small shock to cause someone to fall from a stool or ladder or
roof. Granted that this OSHA directive does not modify the
national code (as of this writing), it is a red flag that should be heeded by everyone
who does electrical work, professionally or otherwise.
I am a realist and also at times been a risk-taker. I know
people will use GFCIs and not ground them! And many people use
those little three-prong adapters and don't attach the grounding
wire or lug to the outlet cover screw.
So be it... I can't control other people's reckless behavior.
Sometimes I can't control my own! Just as long as they realize
they risk a shock hazard when using appliances that require a
ground. It is their responsibility to live with the consequences.
At the least, they should take the NEC's advice and label the
outlet as "ungrounded" or (as a personal option and NOT
specifically recommended by the NEC) disable the grounding hole
with a nonconductive plug of adhesive or epoxy to prevent needless
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