A GFCI will trip even if there is not a current leak to ground. If there is an inductive or physical loss of current, it can also trip. That's why it is legal (acoording to the NEC) to use GFCI's on ungrounded circuits. Many times as an electrican, I ran into situations like that.
Also, most of the extension cords I have seen with the triple tap on the end have VERY bad connections. More than a few times I have seen smoke pluming from the cord when a compressor is plugged in. It is best to avoid the molded triple-tap style cords.
Another note about GFCI's... There are REQUIRED under the following circumstances:
--Outlet is outside*
--Outlet is within 6 feet or a water source
--Bathrooms
--Garages
Another place where a GFCI
protected circuit must be, is when there is a light in a shower area.
*An interesting place where a GFCI outlet is NOT required, is if the outlet is more than 12 feet off the ground. An example would be in a soffit, for Christmas lights. The reason for that is because there is very little chance of anything being plugged into the outlet that is on the ground.
Some of the most stringent GFCI requirements are when hot tubs are involved. A separate GFCI disconnect must be
visible from the hot tub, but
no closer than 5 feet, and
no farther than 50 feet. The inspectors love to nail homeowners for this one.
Here's a copy of my post from another topic on how GFCI's work:
(posted 12-12-00)
Time to go back to my days as an electrician...
First, let's go over the basics on a how a GFCI (Ground Fault Circuit Interrupter) works.
Basically, the GFCI or GFI (same thing) monitors the current flow going in and out of the outlet. And by current, I do not mean voltage... . Rather, I am talking about the wattage/amperage that is flowing in & out of the outlet when an aplliance or something is plugged in. Inside the GFI, there is a microprocessor that does all of the "thinking" to monitor the current flow. It compares the current being used on the "hot" side, and the current coming back on the "neutral" side. For the GFI to trip, the difference between the two has to be greater than a certain amount, which is as low as 5 milliamps (mA). The GFI constantly monitors it, and if a current "leak" is detected, it will actuate a small solenoid inside the housing, cutting off the power to the outlet. The time it takes to do this is very short, about 0. 0002 of a second. Make sense?
The panel-box style GFCI works the same way. However, if you install one of these, make sure the circuit you are using it on is LESS than 250 feet. If it is longer than that, it could trip due to inductive loss of current.
Here's some more info on GFCI's...
Some things have a tendency to trip GFI's more often than others. Lights typically do not trip GFI's. In fact, I have never in my 3 years as an electrician seen one trip due to a light. What does trip them is motorized aplliances/tools. The motors and magnetic equipment can play havoc with the GFI's microprocessor, and casue it to trip. Usually it occurs on startup, which is when there is the greatest chance for current leakage.
So how does this help you when you drop a hair dryer in the tub while giving Fido a bath? Well, the time it takes the GFI to "see" and kill the power, is FASTER than the time it takes for the electricity to fry your dog. Much faster than the standard circuit breaker as well. The regular breaker would trip, but by the time it does that, Fido will be boiled... What it comes down to, is the GFI is a watchdog to make sure you stay alive.
What the GFI will NOT do is protect against shocks, such as taking two bare wires in your wet hands and inserting them into the parallel slots on the outlet. That will nail you pretty good if your hands are wet. If your hands are dry and callused from workin' on a Cummins, then you will feel only a minor shock. Kinda tingly, actually... *LOL*
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[This message has been edited by Evan A. Beck (edited 12-17-2000). ]
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