What The Heck is a GFCI?

Hello everyone, it’s Keith from KB Electric LLC, and I have your answer!


We get a few calls a week with clients requesting a GFCI, GF thinger, a square thing with the push button or simply, “I don’t know what it’s called, the township says I need one.”  That’s ok, I have been saying GFCI for 12 years now and it still rolls off my tongue like R’s in first year Spanish class.


So, quick answer: a ground fault circuit interrupter (GFCI) or Residual Current Device (RCD) is a device that shuts off an electric circuit when it detects that current is flowing along an unintended path, possibly through water or through a person. It is used to reduce the risk of electric shock.  They are required in unfinished basements, bathrooms, kitchens, outdoors or anywhere with in 5 feet of a water supply.


Unlike a fuse or circuit breaker, a GFCI is much more subtle. When you look at a normal 120-volt outlet in the United States, there are two vertical slots and then 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 both of them is called “ground.” If an appliance is working properly, all electricity that the appliance uses will flow from hot to neutral. A GFCI monitors the amount of current flowing from hot to neutral. If there is any imbalance, it trips the circuit. It is able to sense a mismatch as small as 4 or 5 milliamps, and it can react as quickly as one-thirtieth of a second.


So let’s say you are outside with your power drill and it is raining. You are standing on the ground, and since the drill is wet, there is a path from the hot wire inside the drill through you to ground. If electricity flows from hot to ground through you, it could be fatal. The GFCI can sense 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. Pretty cool.


gfci outlet

GFCI Outlet