How Does a GFCI Outlet Work?

Checking the Two Buttons on a GFCI Switch

If you've ever experienced even a second of paralysis caused by electrical shock, it's not a feeling you'll ever forget. In short, you were part of what's called a ground fault.

A ground fault is an instance in which the hot wire touches any area of a grounded device or even the grounded part of a junction box. It can happen in situations when wiring insulation is damaged, perhaps to the mischievous teeth of rodents, or even due to wiring age, or, very commonly, environmental conditions [source: Littelfuse].

Moisture and dampness are two of the biggest causes of ground faults, and the consequences can be life-altering. For example, 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 the ground. If electricity flows from hot to ground through you, the result is a ground fault, and 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 the ground. As soon as the GFCI senses this "leakage" of power, it trips the circuit and cuts off the electricity.

On a final note, understand that GFCI outlets always eventually wear out, so you should test them about once per month [source: McGarry and Madsen]. To test the outlet, press the Reset button, and then plug in a simple night light or other electrical device. The device should turn on. Then press the Test button. If the GFCI is working, the power will immediately be cut. Press Reset again, and your device should turn on again. If so, the outlet is working as it should.

If the light doesn't turn off when you press Test, you have a problem. The GFCI might be improperly installed or malfunctioning, and it won't protect you from shocks. You'll need to replace it or call a professional electrician for help.

You might get about 10 years of use from GFCIs. Realize that older units may fail "closed," meaning they'll still conduct electricity, obviously a dangerous situation that defeats the whole purpose of CFGIs. Fortunately, newer styles fail "open," meaning they'll no longer work, but they won't be a health hazard, either. Either way, test these devices regularly and you'll have extra peace of mind in the family bathroom and beyond.

Last editorial update on May 25, 2018 01:15:20 pm.

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More Great Links


  • Electronic Library of Construction Occupational Safety & Health. "Electrical Safety: Safety & Health for Electrical Trades." January 2002. (April 19, 2018)
  • Fish, Raymond and Geddes, Leslie. "Conduction of Electrical Current to and through the Human Body: A Review." NCBI. Oct. 12, 2009. (April 19, 2018)
  • Littelfuse. "What is a Ground Fault?" (April 19, 2018)
  • McGarry and Madsen Home Inspection. "What is the Average Life Expectancy of a GFCI Receptacle?" (April 19, 2018)
  • Nickel Electric. "Electrical Safety Statistics." May 27, 2015. (April 19, 2018)