Unlike standard electrical outlets, a GFCI outlet constantly monitors the amount of current flowing between the left (hot) and right (neutral) slots. If the GFCI outlet detects even the slightest deviation in the amount of current flowing between these two slots, it trips the internal circuit and cuts off electricity to the outlet.

GFCI outlets have been a requirement of the National Electrical Code in the following situations:· Outdoor receptacles since 1973
· Bathroom receptacles since 1975
· Garage wall outlets since 1978
· Kitchen receptacles since 1987
· Crawl space and unfinished basement receptacles since 1990If your home was built before these dates, they are "grandfathered" and not in any violation of the Code. However, if any remodeling is done to your house in these areas, you are required to update your wiring to meet these standards.

The main reason that a GFCI will detect a deviation in the amount of current is because the wayward electricity is finding another way to the ground instead of through the grounding wire. The other way is usually through a person, also known as a ground fault. This can happen through various means, such as accidentally touching a live wire or dropping an electrical appliance in the bathtub. A GFCI can cut off the power to the outlet within 1/30 of a second, saving a person's life in these circumstances.

There are three types of GFCIs available:· Receptacle. These are installed in the wall where your previous older outlets where located. If installed as the first in a "branch" of outlets (meaning this outlet supplies electricity for standard outlets further down the power line), one GFCI can provide protection for an entire room.
· Circuit breaker. In homes that have circuit breakers installed instead of fuse boxes (like most modern homes), a GFCI can be installed in the circuit breaker to provide protection to the various areas of your home. This has the added benefit as behaving like a fuse, also protecting wires and appliances from overloading.
· Portable. Some extension cord devices have a GFCI built in. If the appliance, tool, etc., is plugged into the extension cord housing instead of the outlet in the wall, the device will provide GFCI protection.