Thread: Testing GFCI

So, when you test a GFCI with the little "test" button, does anyone know what actually happens? I read that the chip creates an imbalance of current, but I'm not sure how it actually does it. Obviously, there is no current sent to ground, since the ground wire is not necessary for the GFCI to work.

I'm talking about on the receptacle itself, not with your hand held tester.

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It depends on the manuf and age of the device, it can get quite technical so here are two links that will give you lots of reading pleasure........


Systems and Methods for Testing Ground Fault Detection Circuitry - Patent application


Self testing ground fault circuit interrupter (GFCI) - US Patent 7443309 Claims

Think like a GFCI

Test circuit. When the "test button" on a GFCI is pushed, a circuit is closed from the hot conductor on the load side of the current sensor to the neutral conductor on the line side of the current sensor. The current flow in the test circuit is limited to slightly more than 6mA. When the "test" button is pushed, the GFCI must detect this differential current, measure it, and signal the trip coil to energize and trip the GFCI. Pushing the "test" button tests not only the trip mechanism but also the complete operation of the GFCI.

The GFCI does not sense a ground fault but rather the imbalance between the hot and neutral conductors so no ground is needed.

I have tested GFCI receptacles with the test button and had the receptacle trip. Then test it with my GFCI tester and find that the receptacle had reverse polarity and the tester will not trip the receptacle. To me the test button on the receptacle gives the person a false sense of security.

Don

Originally Posted by Don Drews

.
To me the test button on the receptacle gives the person a false sense of security.

Don

.
Don,

The Test Button is the Only Recognized Method to Test these devices.
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Originally Posted by Don Drews

I have tested GFCI receptacles with the test button and had the receptacle trip. Then test it with my GFCI tester and find that the receptacle had reverse polarity and the tester will not trip the receptacle. To me the test button on the receptacle gives the person a false sense of security.

Don

Don,

Those are other problems, the GFCI function is best tested with the test button on the GFCI, which does not eliminate testing the receptacles for reverse polarity, etc.

The GFCI test button does not give a false sense of security ... as long as you do the other testing as you normally do anyway.

Gentlemen: Thanks for all your responses. But on to another question, On bathroom receptacle circuits. Years ago they allowed you to daisy chain your bathroom receptacles from one bathroom to another. My understanding of the code now is that when a bathroom receptacle circuit leave that bathroom it can not supply any other devices or receptacle outside that bathroom. Am I understanding the code correctly? I have talked to Master Electricians and get all different kinds of answers. Thanks for your responses. Don

Originally Posted by Don Drews

Gentlemen: Thanks for all your responses. But on to another question, On bathroom receptacle circuits. Years ago they allowed you to daisy chain your bathroom receptacles from one bathroom to another.

You still can.

My understanding of the code now is that when a bathroom receptacle circuit leave that bathroom it can not supply any other devices or receptacle outside that bathroom. Am I understanding the code correctly?

No.

There are two choices: 1) no other receptacles on a bathroom receptacle circuit except bathroom receptacles (from one or more bathrooms); or 2) one circuit to one bathroom and other outlets for other equipment can be on the same circuit (some conditions apply).

For what it's worth, I got curious and called two of the GFCI manufacturers and asked them about the reliability of the test button on some circuit testers. Their answer in both cases was that the only reliable way of testing the GFCI was the internal test of the unit itself. The circuit testers are pretty good but fail often enough to not be considered reliable enough. Also please remember that the newer models since I think 2003 or thereabouts are better protected than the older models that sometimes would fail and still be able to be reset. Hope this is interesting if not helpful.

Originally Posted by Terry Fitzgerald

For what it's worth, I got curious and called two of the GFCI manufacturers and asked them about the reliability of the test button on some circuit testers. Their answer in both cases was that the only reliable way of testing the GFCI was the internal test of the unit itself. The circuit testers are pretty good but fail often enough to not be considered reliable enough. Also please remember that the newer models since I think 2003 or thereabouts are better protected than the older models that sometimes would fail and still be able to be reset. Hope this is interesting if not helpful.

If the tester fails to trip the device, would a faulty blow dryer or razor always trip it?

How would you test a daisy-chained outlet without using a circuit tester?

Sorry, these are questions for them, not for you.

I found a GFCI breaker one time that looked like it was wired in reverse in the panel when the house was built in 1990. It never failed the button test, but it went 20 years without protecting anybody.

I've always been a bit suspicious of the "only approved method of testing is the button" - Of course, the manufacturer is going to say that. What's the alternative? "Sure, we approve testing our product with whatever device you like" - that's just not realistic. No manufacturer of ANYTHING would say that.

I've never taken it to mean the hand testers don't work or aren't reliable.... just that they shouldn't be relied upon if/when they're the only piece of evidence. I've always carried numerous electrical testers in order to try to sort things out when one of them gives a problematic result.

Originally Posted by John Kogel

How would you test a daisy-chained outlet without using a circuit tester?

Plug in your 3 light tester at the downstream duplex and press the test button. If the light goes out it would be protected. You could also use a solenoid type tester between hot and ground on a grounded system.

Here is a link that shows many of the basics of a GFCI receptacle.

Ground Fault Current Interrupters

The article is a bit dated and some opinions are offered that really don't apply, but the basics are sound. What the article doesn't show is newer circuitry that disables the device if it is wired with the hots to the load side.

Check out the first drawing and you will easily see how the internal imbalance test circuit works. If this circuit checks out with the internal test it will work any time an imbalance is present. Keep in mind that the electrical ground at the receptacle often is not the ground path that winds up shocking people and why the lack of it is not an issue for correct functioning of the GFCI.

Just carry a bobby pin, hair pin or whatever you call those things ladies used to pin their hair up with and stick each end into the receptacle. that will let you know if it's working or not!

Originally Posted by Wayne Carlisle

Just carry a bobby pin, hair pin or whatever you call those things ladies used to pin their hair up with and stick each end into the receptacle. that will let you know if it's working or not!

No, it won't!