Did you know that ground fault circuit interrupters work even when installed in older homes that don’t have grounded wiring!
It’s counter-intuitive but it’s true. As you may know, GFCI’s help protect people from getting electrocuted. They are now required at kitchen countertops, bathrooms, outdoors and near other sinks. 3 conductor wiring (with a ground wire), started being used around 1960. It also protects people from electric shock, but it works in a different way. The metal chassis of an appliance in your home is connected to the ground wire in the appliance plug. When this plug is plugged in to a receptacle outlet in a home that has 3 conductor wiring (hot, neutral and ground), the appliance chassis is grounded. If a hot wire in the appliance comes loose and touches the chassis, a very large current will flow for an instant and the house circuit breaker for that circuit will trip off. Thus you won’t get a nasty shock if you touch the appliance.
But how can GFCI’s work in houses that don’t even have grounded wiring? As we said earlier, GFCI's work in a different way. They compare the electric current (amps) going to the appliance on the hot wire with the amps coming back on the neutral wire. If everything is working normally, they should be exactly the same. However, if you touch that chassis we were just talking about (in contact with a loose hot wire) and you’re grounded because you’re washing dishes, in a bathtub, or standing on wet ground, you become another path for the electric current as it tries to get to ground. Now, the amps that are coming back on the neutral wire are not equal to the amps going to the appliance because some of the current has split off and is going through you! In other words you’re getting shocked. The good news is that you’re a smart cookie. Even though you live in an older house with no ground wiring, you listened to your home inspector when he said- “GFCI’s are not required on older homes but they are a safety upgrade. If your budget allows, have them installed”, and you took his advice. Your GFCI has sensed that there is a ground fault and has shut off the electricity. And now you know the truth about GFCI’s. --- Kim Christensen