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Old 07-06-2013, 03:53 PM   #1
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GFCI receptacle sensitivity


Hi;
I have a very old box fan (all metal construction) that does not have a grounding conductor (it has always had only 2 wires in zip cord). The fan is plugged into a GFCI receptacle, and there have not been problems with it.

Today I decided to check on the leakage current, and I found 37mA measured using my Klein Tools multimeter between the fan housing and the receptacle ground conductor. When I measured voltage between same two points I got 40VAC.
When I touch the fan standing on the basement floor in bare feet I do not feel anything.

I just checked on Wikipedia for GFCI and found that 30mA is supposed to be the allowed leakage before trip. Well, if that is the case, then this fan is very close to doing just that; actually it is over the 30mA, but I figure there is a tolerance involved, and I may not be measuring the leakage current properly in the first place.

That said, I feel that there should never be any voltage (and thus the potential for ground leakage current) in any appliance that a human can ever come into contact with. I would not use GFCI as a method to mitigate ground leakage, as I am sure anyone would agree.
Being that this fan is located in the basement next to the treadmill, and could be handled by someone who is damp/wet, I didn't like the situation.
While going out and buying a new fan would have been the easiest thing to so, I kind of like this fan, and doubt I will get anything as powerful for under $100.

So I replaced the 2-wire cord with a 3-wire, which I bonded to the fan's housing using a standard ground screw, and lug for the ground wire (after scraping the paint off of the metal of course).
Now I measure the voltage between the fan housing and the receptacle's GC and I get 0, as I would expect.

Since this fan is around 40 years old, I wasn't surprised to find that there was some leakage, and I am expecting that one day it will start to trip out the GFCI. At that time I will know that it is time to replace the fan.

Any thoughts on this?

Thanks

FW

Edit: I remembered that I have a second unit of the exact same model in storage in the attic, so I took it out and measured its leakage. That one has 50V with abut 50mA leakage to ground. I am getting rid of that one now, but hopefully with the addition of the GC to the other one I can keep using it until the end of the season. Maybe not. That's why I posted here. While I consider myself pretty well educated in electrical, I also have a tendency to overreact to situations like this.

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Old 07-06-2013, 04:02 PM   #2
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GFCI receptacle sensitivity


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Originally Posted by KE2KB View Post
Hi;
I have a very old box fan (all metal construction) that does not have a grounding conductor (it has always had only 2 wires in zip cord). The fan is plugged into a GFCI receptacle, and there have not been problems with it.

Today I decided to check on the leakage current, and I found 37mA measured using my Klein Tools multimeter between the fan housing and the receptacle ground conductor. When I measured voltage between same two points I got 40VAC.
When I touch the fan standing on the basement floor in bare feet I do not feel anything.

I just checked on Wikipedia for GFCI and found that 30mA is supposed to be the allowed leakage before trip. Well, if that is the case, then this fan is very close to doing just that; actually it is over the 30mA, but I figure there is a tolerance involved, and I may not be measuring the leakage current properly in the first place.

That said, I feel that there should never be any voltage (and thus the potential for ground leakage current) in any appliance that a human can ever come into contact with. I would not use GFCI as a method to mitigate ground leakage, as I am sure anyone would agree.
Being that this fan is located in the basement next to the treadmill, and could be handled by someone who is damp/wet, I didn't like the situation.
While going out and buying a new fan would have been the easiest thing to so, I kind of like this fan, and doubt I will get anything as powerful for under $100.

So I replaced the 2-wire cord with a 3-wire, which I bonded to the fan's housing using a standard ground screw, and lug for the ground wire (after scraping the paint off of the metal of course).
Now I measure the voltage between the fan housing and the receptacle's GC and I get 0, as I would expect.

Since this fan is around 40 years old, I wasn't surprised to find that there was some leakage, and I am expecting that one day it will start to trip out the GFCI. At that time I will know that it is time to replace the fan.

Any thoughts on this?

Thanks

FW
5 ma is the trip point...not 30 ma

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Old 07-06-2013, 04:59 PM   #3
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Last edited by Gac66610; 07-06-2013 at 05:01 PM.
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Old 07-06-2013, 05:25 PM   #4
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GFCI receptacle sensitivity


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5 ma is the trip point...not 30 ma
If that's the spec for the GFCI receptacles I am using (Leviton, but not sure which model) then the GFCI is not working, as I measured 37mA from the chassis of the fan to the GC on the receptacle.
Though I don't know how my Klein Tools DMM measures AC current. I'm probably not measuring properly, and should use a GFCI tester if I really want to test the receptacle.

FW
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Old 07-06-2013, 11:28 PM   #5
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GFCI receptacle sensitivity


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...and should use a GFCI tester if I really want to test the receptacle.

FW
The Mfg. says in the instructions,the test button is their suggested testing method on a gfci.
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Old 07-07-2013, 01:38 AM   #6
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GFCI receptacle sensitivity


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Originally Posted by KE2KB View Post
If that's the spec for the GFCI receptacles I am using (Leviton, but not sure which model) then the GFCI is not working, as I measured 37mA from the chassis of the fan to the GC on the receptacle.
Though I don't know how my Klein Tools DMM measures AC current. I'm probably not measuring properly, and should use a GFCI tester if I really want to test the receptacle.

FW
Then I suspect that GFCI is defective and should be replaced.
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Old 07-07-2013, 01:39 AM   #7
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The Mfg. says in the instructions,the test button is their suggested testing method on a gfci.
Hey,,,Bob....
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Old 07-07-2013, 10:39 AM   #8
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The Mfg. says in the instructions,the test button is their suggested testing method on a gfci.
The GFCI does trip when I press the test button, so my method of measurement must be incorrect. I believe I have read previously that simply measuring current between chassis and GC is not a valid test.
I'll leave it be for now. Fan is working, has GC now, and GFCI is not tripping out.

I had thought of buying one of those inexpensive GFCI testers, but from what I know, all they do is exactly what the test button on the receptacle or breaker does, so it would be a waste of money, since I already have a circuit tester (which does not test GFCI function).

FW
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Old 07-07-2013, 10:54 AM   #9
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GFCI receptacle sensitivity


Another issue of over thinking something simple. The receptacle has test button. No meter is required to test a GFCI.

If you are that set on measurements, why not go to night school and become an electrical engineer.
One piece of advice. The GFCI works on the balance of current between the neutral and the hot.

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Old 07-07-2013, 03:37 PM   #10
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GFCI receptacle sensitivity


What kind of meter were you using to measure the leakage current? What is it's accuracy at that range and reading? 37mA should instantly trip any GFCI. The trip point is 5mA, and 37mA is dangerous to a human. Regardless of the "recommended" testing method and whether the test button works or not, the fact of the matter is that a real, confirmed 37mA ground fault MUST trip a properly operating GFCI, and if it doesn't then there is something wrong and it's dangerous. I'd say either the meter is inaccurate in the manner it was used, or the receptacle is wired incorrectly or defective.
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Old 07-07-2013, 10:38 PM   #11
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GFCI receptacle sensitivity


Is 5ma really the trip point ?
If it is ? you must have a lot of nuisance trips ?
Fact is the electrical system is far from perfect, so some leakage will always be around, some times it is beyond your control,as it might be the fault of a neighbours system, or even poco's system.
So with a trip point as low as 5ma, I foresee problems ahead!

In Australia, the trip point on domestic earth leakage breakers (yes I know thats not the correct name for them, but that's the name most people use) is 30ma.
Special class 1 breakers are available with a trip point of 10ma,
but they are only used in hospitals and schools.

Leakage from electric motors is not unusual, especially the older one's,
In the old days grounding took away this small leakage.
But now with the use of gfci's it's now a problem.
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Old 07-07-2013, 10:52 PM   #12
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Old 07-08-2013, 12:17 PM   #13
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Originally Posted by dmxtothemax View Post
Is 5ma really the trip point ?
If it is ? you must have a lot of nuisance trips ?
Fact is the electrical system is far from perfect, so some leakage will always be around, some times it is beyond your control,as it might be the fault of a neighbours system, or even poco's system.
So with a trip point as low as 5ma, I foresee problems ahead!

In Australia, the trip point on domestic earth leakage breakers (yes I know thats not the correct name for them, but that's the name most people use) is 30ma.
Special class 1 breakers are available with a trip point of 10ma,
but they are only used in hospitals and schools.

Leakage from electric motors is not unusual, especially the older one's,
In the old days grounding took away this small leakage.
But now with the use of gfci's it's now a problem.
5mA is the maximum leakage current allowed for a GFCI. 30mA is for GFPE, which is not used in residential settings. There is no way for POCO or neighborhood problems to affect this. It does not detect current on the grounding conductor. GFCIs detect the imbalance of current between the hot and neutral conductors passing through the device. Only an actual ground fault downstream of a GFCI can trip a GFCI.

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