One of the most common electrical devices I replace in a home is the GFI. The GFI or GFCI Ground Fault Circuit Interrupter device's only reason for existence is to prevent electrical shock or worse, electrocution. The definition of electrocution is death by electrical shock.
Technically, the GFCI senses the electrical current flowing between the electrically hot wire and the ground wire. This electrical current should be equal. If the electrical current flow is not equal, even 3 to 4 milliamps difference, it will trip in less than 1 second.
For example, if you are using a hair dryer and because it somehow gets wet and some small part of the electrical current flows through your body instead of through the GFCI, then it will open the circuit and shut off current flow to the hair dryer.
You should find these devices where ever there is a chance you may come in contact with electricity and water, such as the kitchen, bathroom, unfinished basement, outdoors, and in your garage.
There are 3 main types in use in homes and businesses today. The 1st is the wall plug (see photo). The second is a device used on extension cords and is mobile and easy to use anywhere, and the third is in your breaker panel.
My final comment on these lifesaving devices is that they should be tested monthly. To test them, trip the button marked test, and then reset it with the button marked reset. If it will not trip, or it will not reset, have a qualified electrician check it out for you. These devices are often at the head of a circuit that controls many other receptacles, if they are not wired correctly into the GFCI, it and they will not be protected.
Jonathan Smith has been in the Air Conditioning and Heating industry for well over 30 years and has spent more than 27 years in the Electrical industry.