Ground Fault Circuit Interruption or a GFCI is a protection device for electrical circuits. Most often observed in wet or damp locations such as a kitchen, bathroom, laundry room or outside. Their usage has grown in recent years. The most common place to see a GFCI has been at individual receptacles. A common protection method used in newer home circuits is to install a GFCI circuit breaker.
A basic circuit breaker will allow power to pass through it until the amount of power used exceeds a set limit. For example, a kitchen outlet protected by a 20 amp breaker would be able to run a microwave that draws 15 amps of current. If you attempt to use an 8 amp blender at the same time as the microwave, the total draw is 23 amps, which exceeds the 20 amp circuit breaker capacity. The breaker will trip to protect your wires from overheating.
But what happens if water splashes into the receptacle from your sink? Pure water isn’t actually a great conductor (but make no mistake, it is a dangerous combination). So you have water that is creating a path between your wire conductors which allows SOME power through (this is called a short). For simplicity, let’s say the short allows 1 amp of power leakage. That breaker will not trip by itself because 1 amp does not exceed the 20 amp rating of the breaker. The breaker won’t even trip if there is a microwave running at 15 amps plus 1 amp of loss through the water. Touching the water or metal pipes would be dangerous as they actively have power traveling through them.
So we install GFCI protection. In a very simple sense, normal breakers measure the power going out only. GFCI breakers differ because they measure power coming back in as well and compare them for a discrepancy. Power travels in a circuit out one side and returning through the other side. If there is enough difference between the amount of power leaving the GFCI and returning to it, the GFCI will discontinue power until you reset it. The important thing is: if power leaves the GFCI, but a short occurs and causes some power to exit through a metal water pipe, a bathtub, or the earth itself – the GFCI is aware that something went wrong, and it protects you.
GFCIs must be tested monthly or according to manufacturer directions, and they do have a limited life expectancy. When they fail, older GFCI receptacles may stop providing protection yet still provide power, so you wouldn't know there is a problem without testing. Newer GFCI receptacles just stop providing power altogether. GFCIs must be installed by a licensed electrician – I have seen too many which were installed by DIY owners that appear to work properly, but they do not provide protection due to improper wiring. You might even think they work because the built-in test functions work – but there are different ways to wire GFCIs which could trick someone into thinking they have full protection but only have a portion of protection. This is why we carry our own testers – they test real life situations with a very fine accuracy point.
Too long, didn’t read version: GFCIs keep you safe and monitor if you have power loss or short circuits.
-Marshall Tramp, CPI, RMP
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