It's time to winterize...

PartyOf Five wrote:
You're right.. that GFI circuit would only cut power if the wiring overheated- I'll have to ask what they traced his back to, was years ago.

Well, that's not the way GFCI's work. GFCIs (ground fault circuit interrupters) are devices used to protect humans from electrical shock. They DO NOT offer any protection for over current situations. That's what a circuit breaker/fuse is designed to do.

A GFCI will "trip", that is, disconnect the power to the hot line, when the difference current between the hot line and the neutral line exceeds about 5 mA (5 thousands of an amp). Normally, those two lines carry the exact same current. But IF there should be an imbalance more than about 5 mA, the device will open to protect against line-to-ground shocking hazards. That imbalance of current means that somehow current is being returned to the source by a path OTHER THAN the neutral, and it quite likely could be through a person. The 5 mA imbalance is in effect whether the GFCI is passing 1/10 of an amp or 15Amps. It doesn't matter to the device. Only the difference in the current in each line determines whether it will trip or not.

For comparison, possible heart fibrillation can occur at about 100 mA at 60Hz AC. Most 120VAC breakers are 15 or 20 Amps, so lethality has set in long before the main breaker would trip...if it ever tripped. At 5 mA, when the GFCI is set to trip, the person will feel the shock but voluntary muscle control is maintained, so they can let go of whatever is shocking them, though the GFCI should open the circuit in less than 1/10 of a second.

Someone had noted above that the resistance might change in a device and the GFCI would offer protection. That is untrue. The resistance of a heater element varies constantly with temperature. It's "cold" resistance is less than its "hot" resistance. With age electrical characteristics also change, but there's no "shocking" hazard associated with this UNLESS the insulation of the appliance is somehow compromised. A GFCI would not respond to a change in resistance (load) of an appliance or device. The GFCI only reacts to a slight imbalance of current between hot & neutral. Now if the insulation in the appliance had a failure and that allowed the hot line voltage to be contacted by someone, the GFCI should sense that and shut-down the circuit. IF the appliance had a wired ground connection to it's chassis (3-prong circuit), and the insulation fault allowed the line voltage to contact the grounded chassis, THAT would (should) cause the circuit breaker to trip back at the panel as the current would spike high with the short circuit. BUT...the GFCI will probably not do anything in this case.

And just to complete matters, there are circuit breakers which include GFCI's in their construction which reside in the electrical panel. These devices provide over-current protection via the breaker and shock protection via the GFCI.

In general: GFCI's protect people, Circuit Breakers protect the wiring.

Oh, one last thing. GFCI's do, on occasion go bad. They should be tested at least once per month using the "Test" and "Reset" buttons on them. Just be aware that other outlets downstream might also be wired to be protected by that GFCI outlet and testing (tripping) it will disconnect power to those outlets as well. Not funny if the person is jogging on a treadmill plugged into said protected outlet at the time. Well...not funny at the time. NOW it's funny as heck to think back on!!! LOL

Be safe everybody!!!

~Rick