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Old 12-11-2008, 08:29 AM   #1
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One of my GFI's was tripped this morning and when I reset it it holds for 5-10 sec and then pops again. I unplugged everything and it is still doing it, does this mean the GFI is bad?

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Old 12-11-2008, 09:10 AM   #2
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Could be bad or if it is attached to an outdoor recpetacle there could water or insects in the receptacle box. Test be removing any wires connected to the LOAD terminals. If it resets then problem is in the LOAD circuit.

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Old 12-11-2008, 09:14 AM   #3
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GFCI receptacle devices aren't high grade hardware, and do break or go bad. Sometimes replacing them with a new GFCI device will take care of the problem.

If the problem persists, your GFCI might be functioning properly and revealing a deeper problem.

The 10 second delay in tripping makes me think the device is bad.
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Old 12-11-2008, 09:22 AM   #4
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I would take Joed's advice and disconnect wires from the LOAD terminals. There could be a small amount of leakage that is causing it to trip after a short time. Of course it could also be a bad GFCI, but either way, you have to open the box and take a look.
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Old 12-11-2008, 09:45 AM   #5
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Quote:
Originally Posted by tedrjar View Post
it holds for 5-10 sec and then pops again.
There's 6mA to 4mA leakage, according to the UL GFI (maximum) curve. With real world GFIs the current probably has to be higher than this to trip within those intervals.
With this much leakage, you might be able to measure it with an ohmmeter (less than 30 KΩ fails).
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Old 12-11-2008, 07:28 PM   #6
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You need a digital meter on the 200vac scale. 10 MΩ input impedance for the meter is assumed for this test.

120.0vac is in series with the meter in series with the hot lead of the cable or device under test. The grounded lead of the cable or device under test returns the current to the source.

A: If the cable or device is shorted to the ground lead, you read 120.0vac.
B: If the perfectly good cable is 50' long, you read 114.3v due to normal cable capacitive reactance. Longer cables will read closer to 120.0v.
C: If the cable has enough leakage to trip a GFI within seconds, you read 119.6v.

If you shunt the digital voltmeter with a 1MΩ resistor, your readings will be
A: 120.0v
B: 80.0v
C: 116.5v

If you use a 1000Ω/volt cheapie analog meter, no shunt resistor, your reading will be (on the 150v scale)
A: 120.0v
B: 28v
C: 100v

There is no danger of blowing the meter, even if the cable is shorted.

You can see that using the cheaper meter gives you a more sensitive test.

If the cable or device passes this test, the cable or device is almost certainly not the cause of the GFI tripping.

Last edited by Yoyizit; 12-11-2008 at 07:34 PM.
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Old 12-12-2008, 02:15 AM   #7
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Quote:
Originally Posted by Yoyizit View Post
You need a digital meter on the 200vac scale. 10 MΩ input impedance for the meter is assumed for this test.

120.0vac is in series with the meter in series with the hot lead of the cable or device under test. The grounded lead of the cable or device under test returns the current to the source.

A: If the cable or device is shorted to the ground lead, you read 120.0vac.
B: If the perfectly good cable is 50' long, you read 114.3v due to normal cable capacitive reactance. Longer cables will read closer to 120.0v.
C: If the cable has enough leakage to trip a GFI within seconds, you read 119.6v.

If you shunt the digital voltmeter with a 1MΩ resistor, your readings will be
A: 120.0v
B: 80.0v
C: 116.5v

If you use a 1000Ω/volt cheapie analog meter, no shunt resistor, your reading will be (on the 150v scale)
A: 120.0v
B: 28v
C: 100v

There is no danger of blowing the meter, even if the cable is shorted.

You can see that using the cheaper meter gives you a more sensitive test.

If the cable or device passes this test, the cable or device is almost certainly not the cause of the GFI tripping.
Let me know when you write a book. I want to buy it.
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Old 12-12-2008, 07:09 AM   #8
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Quote:
Originally Posted by Yoyizit View Post
There's 6mA to 4mA leakage, according to the UL GFI (maximum) curve. With real world GFIs the current probably has to be higher than this to trip within those intervals.
With this much leakage, you might be able to measure it with an ohmmeter (less than 30 KΩ fails).

No, a good GFCI will definately trip at those levels, I have tested hundreds with the tester in the following post.
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Old 12-12-2008, 07:12 AM   #9
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Quote:
Originally Posted by Yoyizit View Post
You need a digital meter on the 200vac scale. 10 MΩ input impedance for the meter is assumed for this test.

120.0vac is in series with the meter in series with the hot lead of the cable or device under test. The grounded lead of the cable or device under test returns the current to the source.

A: If the cable or device is shorted to the ground lead, you read 120.0vac.
B: If the perfectly good cable is 50' long, you read 114.3v due to normal cable capacitive reactance. Longer cables will read closer to 120.0v.
C: If the cable has enough leakage to trip a GFI within seconds, you read 119.6v.

If you shunt the digital voltmeter with a 1MΩ resistor, your readings will be
A: 120.0v
B: 80.0v
C: 116.5v

If you use a 1000Ω/volt cheapie analog meter, no shunt resistor, your reading will be (on the 150v scale)
A: 120.0v
B: 28v
C: 100v

There is no danger of blowing the meter, even if the cable is shorted.

You can see that using the cheaper meter gives you a more sensitive test.

If the cable or device passes this test, the cable or device is almost certainly not the cause of the GFI tripping.
Your numbers will never be that, the voltage to your house can be anywhere from 110 to 130 volts, it jumps all over depending on the time of the day. Also the resistance of your meter leads, the resistance of your connection points, the tolerance of your shunt resistors, etc, ect, ect..........

Or, you can just get one of the following and not waste your time trying to scab together something that is already available:
Attached Thumbnails
Gfi-img_0982.jpg  

Last edited by Silk; 12-12-2008 at 07:26 AM.
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Old 12-12-2008, 02:57 PM   #10
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Quote:
Originally Posted by Silk View Post
Your numbers will never be that, the voltage to your house can be anywhere from 110 to 130 volts, it jumps all over depending on the time of the day. Also the resistance of your meter leads, the resistance of your connection points, the tolerance of your shunt resistors, etc, ect, ect..........

Or, you can just get one of the following and not waste your time trying to scab together something that is already available:
What make and model is the tester in the picture?
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Old 12-12-2008, 03:00 PM   #11
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Quote:
Originally Posted by Timster View Post
Let me know when you write a book. I want to buy it.
Thanks.
I thought I could write until I got onto Internet forums. I come to find out that it's not that easy to write what I mean. . .
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Old 12-12-2008, 05:11 PM   #12
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Quote:
Originally Posted by Yoyizit View Post
What make and model is the tester in the picture?

It's a Hubbell GFT2G

Now if I wanted to test the cable I would:

1. Turn off the breaker
2. Use an ohmmeter between hot and ground
3. Use an ohmmeter between neutral and ground
4. If I have less than 120/.004=30,000 ohms between either conductor and ground, I would know the cable was tripping the GFCI.

Simple, Easy, No special setup required.

Here's a rule that I live by, it's called KISS

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Works for me.
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Old 12-12-2008, 05:36 PM   #13
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[QUOTE=Silk;197261]It's a Hubbell GFT2G
QUOTE]

Kinda pricy for a diy'er
I have never seen one like that
How does it work
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Old 12-12-2008, 06:43 PM   #14
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The numbers 1 - 6 on the end correspond to 1 through 6 milliamps. As you turn the dial it diverts 1 to 6 milliamps to ground. If the GFCI doesn't trip by the time you get to 6, the gfci doesn't work.
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Old 12-13-2008, 03:56 AM   #15
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I just cut the end off one of the millions of computer IEC power cables I have and then put 2 x 22kohm 1/2 watt resistors in parallel between ground and hot for a total of 11kohm 1 watt. Works great for testing GFCIs and confirming that downstream outlets are protected. Gives you about 10ma from hot to ground.

Total cost, a few cents. :P


If you want exactly 6ma, it should be about 20,000 ohms. I would use 2 x 1/2 watt in parallel (remember that cuts the ohms in half), they don't dissipate much power even in an unprotected outlet, but good to make it safer, in case some idiot leaves it plugged in..


Last edited by Gigs; 12-13-2008 at 04:00 AM.
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