GFCI Protector


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Old 11-08-03, 04:09 AM
T
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GFCI Protector

In school we had to build a simple GFCI protector. Its just a box with a SPST switch connected to a GFCI outlet.

Black went to the switch with a switch leg to the outlet. Neutral went directly to the outlet.

Under the wire nut of the ground I had three legs: one going to the switch ground, one going to the outlet ground, and one going to the box.

It checked out OK and I got the button to pop on all tests except for one:

(controlled environment) I took a piece of wire and stuck one end in the hot slot of the outlet and touched the other end to the box. Yow, fourth of July. It arched and melted the wire right to the box.

However, it didn't trip the GFCI but it did trip the breaker.

Anybody know why this happened?

Tripper
 
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Old 11-08-03, 04:42 AM
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Consider that the GFCI receptacle's only job is to open the circuit when it detects more than 10mA difference of current between the hot and neutral. In your experiment, there would have been a lot of current on the hot and none on the neutral, so it should have tripped.
So I will guess that the GFCI receptacle was not operating properly and requires replacement.
 
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Old 11-08-03, 08:31 AM
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When the test button trips the GFCI but a ground fault does not the most likely cause is that you wired the line to the load terminals of the GFCI. Doing that will cause the outlets that are built into the GFCI mechanism to be on the line side of the gfci detecting mechanism so the fault detecting mechanism never sees the fault current.
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Tom H
 
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Old 11-08-03, 08:46 AM
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Testing a GFCI safely!

When you test a GFCI you should not do it by creating a dead or bolted fault. There are four completely safe ways to test a GFCI that I know of.

Use a plug in circuit polarity tester that has a test bottom on it. The test bottom connects a resister between the hot terminal of the tester and the ground pin of the tester. This test will only work when there is a Equipment Grounding Conductor connected to the receptacles green octagonal grounding conductor terminal that has a low enough impedance to conduct the 6 milliamperes of test current back to the Xo of the source.

Use a resister to simulate a fault. The resister should be sized to pass 6 milliamperes at 120 volts. That would be 2K ohm IIRC.

Apply a solenoid circuit tester; such as a Wiggy; between the receptacle hot slot and the receptacles ground hole. Since the commercially available solenoid testers draw about 7 milliamperes at 120 volts this is a great field expedient test of the GFCI function.

Use a Sure test circuit tester which has a resister much like the plug in polarity testers.
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Tom
 
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Old 11-08-03, 04:00 PM
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When you cause a fault that has the potential to trip multiple breakers or multiple GFCIs or some combination of the two, it a race to see which one trips first. Repeat the test ten times and you might get ten different results. When one trips, the others have no need to trip.
 
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Old 11-08-03, 04:35 PM
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I think Hornetd got it correct. You connected to the load terminals. The gfci should have tripped if it was connected properly.
 
 

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