A ground fault interrupter outlet, or GFI outlet, is designed to protect people from electric shock. GFI outlets have three holes in a triangle pattern; there are two vertical slots and a round hole between them The shorter slot is called the “hot,” the longer slot is the “neutral” and the round hole is called the “ground.”
Typically, all electricity will flow from the “hot” slot through an appliance plugged into the outlet, and back into the “neutral” slot. The GFI outlet monitors the current flowing to and from the appliance. If the outlet senses an imbalance in the current flowing from the hot to the neutral slots, it will disconnect electricity flowing to the outlet. Most GFI outlets are very sensitive, and are capable of detecting a current imbalance of just a few milliamps.
Such an imbalance generally means there is a current leak somewhere-the worst case scenario being that the missing current is flowing into a human, instead of back to the neutral outlet. GFI outlets shut off current quickly, in less than one-tenth of a second, so that extra current will not flow where it’s not supposed to.
It can be difficult to know if you have GFI outlets in your home just by looking at them. They are recommended in areas of a building where there is water, because moisture increases the risk of electric shock (picture someone dropping a hairdryer into the sink). A few decades ago, they generally were only installed around pools and boathouses, but now are commonly found (and required by building code in Alaska) in places like bathrooms, garages, kitchens, crawl spaces, unfinished basements and outdoor outlets.
Heat tape should be plugged into a GFI outlet because heat tape is typically protecting water pipes and therefore has the potential to be exposed to moisture.
Some GFI receptacles have test/reset buttons on them. You can check if the GFI protection on these outlets is working by pushing the test button — which should shut off the current to any device plugged into the outlet. Pushing the test button will also cause the reset button to pop out. You can turn the outlet back “on” by pressing the reset button. GFI outlets can fail as power surges from the utility can damage their internal circuits, so testing them occasionally is a good idea.
Other outlets have GFI protection at an “upstream” outlet or at the distribution panel and may have no test/reset button. In this case, to test a specific outlet, you will need to push the test/reset buttons on the upstream outlet or at the distribution panel.
Installing GFI outlets
It’s just as easy as installing a regular outlet, though you need to pay attention to ensure the proper terminals are connected to the source. It takes a little extra consideration to wire it up if you are using it to protect outlets downstream.
GFI outlets cost more to install than regular outlets. While a regular outlet can cost as little as a few dollars, GFI outlets can cost more than $20. This adds up when considering every outlet in a home and explains why electricians may install GFI protection at the panel rather than at each individual outlet.
A similar type of outlet is an arc fault circuit interrupters (AFCI). These are required in the living room, bedrooms, hallways, at lighting circuits, and use a special circuit breaker at the distribution panel. While GFIs are designed to protect you from shock, AFCIs are designed to prevent fires when an electrical arc is caused by, for example, driving a nail into the wall and hitting a wire. GFI receptacles cannot be used on an AFCI circuit.