What is GFCI — Ground-Fault Circuit Interrupters

The code requirement to install GFCIs has been a real lifesaver for homeowners. One government statistic suggests that a GFCI installed in every home in America could prevent more than two thirds of all residential electrocutions. A GFCI measures the current flowing into the outlet through the black or hot wire and the current outflow through the neutral or white wire (see the following figure). If the GFCI detects any difference greater than 7 milliamps, it shuts off the current. Why? Because any difference in the current is an indication that the current is somehow shorting or “leaking”—maybe through you! It might be a short in an appliance such as a hair dryer or an electric mixer. These are dangerous situations, and a GFCI will shut down far faster (in as little as 1/40 of a second) than a standard circuit breaker or fuse.
An older home may or may not have GFCIs, but it can be retrofitted with them. A GFCI won’t always prevent an initial shock, but it does prevent a lethal one. The current NEC calls for GFCIs to be installed in a number of locations, including …

• Bathrooms.
• Kitchen counters.
• Outdoors.
• Garage walls.
• Unfinished basements and crawl spaces.

Why have these areas been singled out? They all have something in common: water or water pipes, both of which are good at seducing a current away from its righteous path back to your panel or fuse box to take a trip through your body instead. There’s a reason why various cads in the movies get knocked off while in the bathtub when an irked female character throws a plugged-in curling iron into the water. If you use a defective hair dryer when touching the water faucet in your own bathroom, you’ll be glad you have a GFCI installed.

A modern electrical system will have GFCIs in the form of either outlets or breakers, although the latter are more expensive. The presence of a GFCI in an old system is a demonstration that a past owner was concerned enough to attempt at least a partial modernization of the system.