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Old 12-14-2008, 11:24 AM   #1
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GFCI test with analog meter


Goodmorning.

I know we recently talked about expensive $200 GFCI testers here, and also how to build them. I found if I take my old analog meter, and just use that to test hot to ground, it opens the gfci. Is there any way to know how many mw this would be equivalent to?

It seems like a reasonable way to verify your wiring on a new install. If all outlets open the GFCI when the tester is inserted like this, you know it is all wired correctly. I just don't know the level in which the GFCI is tripping. Which I guess is unlikely to be a issue that really needs testing since these are new GFCI's I am testing.

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Old 12-14-2008, 11:34 AM   #2
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GFCI test with analog meter


So your analog meter presents less than 30kΩ to the circuit under test on the 150v range? This is 200Ω/volt sensivity.
Where did you get such an insensitive meter?


Last edited by Yoyizit; 12-14-2008 at 11:44 AM.
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Old 12-14-2008, 11:40 AM   #3
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GFCI test with analog meter


The ONLY proper way to test a GFCI is by using the test button on the device itself, GFCI testers do not exist, they only make GFCI indicators. big difference.
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Old 12-14-2008, 11:55 AM   #4
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GFCI test with analog meter


Quote:
Originally Posted by chris75 View Post
GFCI testers do not exist, they only make GFCI indicators. big difference.
Please elaborate.
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Old 12-14-2008, 11:55 AM   #5
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GFCI test with analog meter


Quote:
Originally Posted by Yoyizit View Post
So your analog meter presents less than 30kΩ on the 150v range? This is 200Ω/volt sensivity.
Where did you get such an insensitive meter?
I have no idea where it came from. This is the meter:
http://www.azpartsmaster.com/Product...A__MM2800.aspx

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Old 12-14-2008, 11:55 AM   #6
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GFCI test with analog meter


No, don't bother.
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Old 12-14-2008, 11:57 AM   #7
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GFCI test with analog meter


Quote:
Originally Posted by Yoyizit View Post
No, don't bother.
I am sure I am missing something here.

Re Testers: The things were were discussing here the other day,

http://www.drillspot.com/products/15...2G_Gfci_Tester

"Hubbell GFT2G Gfci Tester"

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Old 12-14-2008, 12:00 PM   #8
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GFCI test with analog meter


Quote:
Originally Posted by jamiedolan View Post
I have no idea where it came from. This is the meter:
http://www.azpartsmaster.com/Product...A__MM2800.aspx

Jamie
Yeah, it's a solenoid type, a "Wiggie" or a "Wigglesworth."

I was unable to find out how much current these things draw depending on the voltage into them. From your results it is probably more than 4mA, maybe between 1mA and 4 mA.
The advantage is that they are rugged, and may not respond to phantom voltages. For household use they are ideal except for the GF tripping, which may be a plus or a minus, depending on what you're after.

When I want to trip a GF I use my 4w test lamp, otherwise my 10MΩ DVM.

BTW, anything (and anybody) can be tested.
The problem with go/nogo testing is the rate of false positives and false negatives. Lie detectors and pregnancy tests have these, and the way around them is repeated testing.
With a certain electrical device that shall remain unnamed that uses "signature analysis" I'd think this false indication problem is almost insurmountable.

It's worse than that.
Speaking of signal analysis, your attack helicopter receives a signal that you are being targeted for a guided missile.
You believe the homing signal comes from the building below, so you fire your minigun (100 rounds per second) at the building, reducing it and the people therein, to dust within seconds.

Oops! False positive! Sorry!

Would you rather have a false negative, where your signal detection thing just sits there and doesn't warn you of a perfectly valid signal?

Who decides an "acceptable" rate for false positives and false negatives, in warfare or with AFCIs?
Not me, that's fer' sure.

Last edited by Yoyizit; 12-14-2008 at 12:15 PM.
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Old 12-14-2008, 12:06 PM   #9
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GFCI test with analog meter


Quote:
Originally Posted by Yoyizit View Post
Please elaborate.
Um, they dont make a GFCI tester.
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Old 12-14-2008, 12:11 PM   #10
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GFCI test with analog meter


Quote:
Originally Posted by KE2KB View Post
You need another meter, more sensitive than the one you are measuring the resistance of.
Set your old meter on the correct scale (150VAC).
Use the sensitive meter to measure the resistance across the old meter's leads. That should give you an accurate reading of the old meter's resistance on that scale.
Now, just use ohm's law to figure the current: I=E/R

Edit: You could do it without the second meter if you just place a known resistance in series with the meter's lead, and apply a known voltage to the circuit.
The voltage your meter reads will be equal to I x R, where R is the resistance of your meter, and I is the current through the circuit.
Since current in a series circuit is the same through each resistance, you can calculate I by: I=E/R, where E is the voltage across the known resistance (which would be the result of the applied voltage minus the voltage your meter reads), and R is the known resistance.
Your meter resistance is then it's reading divided by the current calculated in the previous step.

The problem with this method is that, since your meter needs to be in the 150VAC scale, your applied voltage will have to be fairly high (I would say 50V or higher) to get a decent reading on the meter, so you could be shocked!
The analog meter does not have any different settings. Just touch the leads and it's hot or not and it shows you a reading from 0 to 600v.

I will check what the resistance reading is with a digital meter. What setting do I want to use to test the resistance? Whatever the most sensitive option is on the digital meter?
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Old 12-14-2008, 12:19 PM   #11
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GFCI test with analog meter


Here's a GFCI indicator/tester. Not sure it would really qualify as a tester though.

http://contractorservices.homedepot....d-a1f66ab3a4a2
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Old 12-14-2008, 12:19 PM   #12
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GFCI test with analog meter


Quote:
Originally Posted by chris75 View Post
Um, they dont make a GFCI tester.

Um, yes they do.
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Old 12-14-2008, 12:21 PM   #13
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GFCI test with analog meter


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Originally Posted by jamiedolan View Post
The analog meter does not have any different settings. Just touch the leads and it's hot or not and it shows you a reading from 0 to 600v.

I will check what the resistance reading is with a digital meter. What setting do I want to use to test the resistance? Whatever the most sensitive option is on the digital meter?
Jamie
I thought it was an analog meter.
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Old 12-14-2008, 12:24 PM   #14
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GFCI test with analog meter


Apparently chris75 has drank the UL/CB manufacturer kool-aid. They don't like to call them testers, because then they might have some obligation to make sure that their product actually works right with them.

Basically, when they come out with a new CB/outlet that fails with common testers because the tester might not produce the same test conditions they used, instead of fixing their product, they just call the tester an "indicator" and say to use the internal test button...

It's a big cop-out on the manufacturer's part.
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Old 12-14-2008, 12:28 PM   #15
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GFCI test with analog meter


Quote:
Originally Posted by KE2KB View Post
I thought it was an analog meter.
The meter that trips the GFCI is a analog meter. I thought you were saying I could test the analog meter with a digital meter to figure out how many MW are being pulled from the analog meter?
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