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Overview: We hear talk about safe electrical outlets that will trip the circuit breaker if there is a short circuit in the appliance we have plugged into it. These electrical outlets are called GFCI outlets. Ok, what is a ground fault circuit interrupter (GFCI) outlet and how does it work. There are two types of GFCI used in houses, a GFCI circuit breaker that is installed in the electrical panel and the GFCI outlet where the circuit interrupter is built into the outlet. GFCI electrical outlets are used more often that GFCI circuit breakers because a GFCI electrical outlet is much less expensive than GFCI circuit breakers.  A GFCI outlet protects people from electrical shock if there is a short circuit. It is much different than a fuse. The function of a fuse is to protect a house from an electrical fire. A basic 110 volt electrical circuit consists of three wires; a black wire called the hot or load (sometime it is a red wire), a white wire that is the neutral, and a ground wire that is either plain bare copper or green.If the hot wire were to accidentally touch the neutral wire for some reason an incredible amount of current will flow through the circuit and start heating it up like one of the coils in a toaster. The fuse, or circuit breaker, heats up faster than the wire and the fuse burns out or the circuit breaker trips to the off position before the wire can start a fire. Short circuits can be caused by a variety of reasons such as a mouse chews through the wire insulation, a nail is driven through the wire while hanging a picture, or the vacuum cleaner sucks up a lamp cord and cuts it.
A GFCI outlet works
in a more subtle way. When you look at a normal 120-volt
outlet there are two vertical slots and a round hole
centered below them. The left slot is slightly larger than
the right. The left slot is called "neutral," the right slot
is called "hot" and the hole below them is called "ground."
If an appliance is working properly, all electricity that
the appliances uses will flow from hot through the appliance
and back to neutral. A GFCI monitors the amount of current
flowing from hot to neutral. If there is an imbalance, or
difference between them the GFCI outlet trips the circuit at
the outlet. It is able to sense a mismatch as small as 4 - 5
milliamps, and it can react as quickly as 1/13 of a second.
For illustration
purposes, say you are outside with your power saw and it is
raining. You are standing on the ground, and since the saw
is wet there is a path from the hot wire inside the saw
through you to ground. If electricity flows from hot to
ground through you, it could be fatal. The GFCI senses the
current flowing through you because not all of the current
is flowing from hot to neutral as it expects. Some of it is
flowing through you to ground. As soon as the GFCI senses
that, it trips the circuit and cuts off the electricity. The
amount of current flowing through you to ground is very
small, 5 milliamps, which you will not feel. There is little doubt that GFCI electrical circuits will protect you from harm and your equipment from damage. I recommend GFCI circuits for all garage, workshop, and outdoor electrical circuits.
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