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Old 05-28-2010, 10:32 PM   #31
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Must be Levitons...


Quote:
Originally Posted by secutanudu View Post
What manufacturer gfci do you have? Mine is a Leviton 15A from home depot. I have some in the house from lowe's - I think cooper. I'll try swapping them.

Also - I think it only trips when flipping the switch slowly.

Maybe a different switch - like a fancy timer switch - would help.
I am having the same issue in my daughter's bedroom with a ceiling fan. I replaced a non-grounded outlet with a Leviton SnapLock (might not be the right name, threw out the package). The fan is on the load side of the circuit from the GFCI. When the fan is turned off the GFCI trips. I've replaced the GFCI with another Leviton and same issue. Moved the old GFCI to the bathroom and had no issues with it. I also replaced the switch for the fan and this also made no difference.

Its not consistent either. It seems to not trip if the lights in the fan are turned on when I turn off the switch. This is leading me to believe when I turn of the switch with the fan on, the fan is essentially becoming a generator and putting a voltage on the wire to the switch which the GFCI is somehow picking up and tripping. With the lights on, the voltage is dissipated.

(first post on the forum, so sorry if its long... been searching this forum for a while looking for a couple of issues I have. This is one of them so if the Cooper idea works, I know where I can get one).
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Old 05-29-2010, 10:07 AM   #32
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Quote:
Originally Posted by tdeg807 View Post
When the fan is turned off the GFCI trips.
It seems to not trip if the lights in the fan are turned on when I turn off the switch.
GFCIs are supposed to trip when they sense a current difference. The trip time depends on the current, according to T = (20 / I)^1.43, so 20 mA of leakage current will trip in less than one second and 5 mA will trip in less than 7 seconds.

Anyway, this current difference is a 'differential mode' signal.
When the current in both lines changes equally, like when you turn something on or off, this is a 'common mode' signal and is supposed to be rejected by the GFCI. The higher the 'common mode rejection ratio' the better the device does its job.

The current change in both lines is larger when there are no other loads on the GFCI, so if you have a steady load of a few amps the fan turning off won't make that much of a difference.

I was unable to find GFCI patents relating to methods of getting around these spurious responses to large, abrupt, common mode signals. If you can find some, like by Googling
GFCI
the assignee company is a probably a good place from which to buy one of these.

Good addt'l search keywords would be
abrupt
change
current
nuisance
false
rejection
large
load
differential

BTW, if you have a good idea, others will steal it. It's the way of the world!
http://ewweb.com/mag/electric_leviton_wins_gfci/

Last edited by Yoyizit; 05-29-2010 at 10:22 AM.
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Old 05-29-2010, 10:39 AM   #33
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Quote:
Originally Posted by Yoyizit View Post
GFCIs are supposed to trip when they sense a current difference. The trip time depends on the current, according to T = (20 / I)^1.43, so 20 mA of leakage current will trip in less than one second and 5 mA will trip in less than 7 seconds.
You might want to compare your "facts" vs the published specs provided by Hubbell. Hubbell state the response times at .025 seconds. I guess you could say that .025 seconds is less than 7 seconds, but I wouldn't want to depend on your "stats". Are you even aware of the amount of damage that could be done if UL allowed trip levels like you allege?

Here is the link, check the bottom of page 3.

https://www.hubbellnet.com/max_htm/P...rary/h4511.pdf
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Old 05-29-2010, 12:12 PM   #34
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--Trip Times--


Yoyizit is correct about GFCI's not tripping instaneously.
While GFCI's will typically trip in 25 ms or so at fault currents exceeding 20 to 30mA, they are permitted by UL to take several seconds to trip at fault currents in the 6mA range.


Source:
http://ecmweb.com/mag/electric_think_gfci/
Ref: 2nd paragraph after Why GFCI's

The Hubbell Spec qualifies their 25mS number by adding Nominal
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Old 06-27-2010, 10:53 AM   #35
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this is an interesting topic Yoyizit. where dose 1.43 come from? at first i thought you meant peak current, which is 1.41, but you seem firm on 1.43.

as for minding against spurious faults at turn on, what i think is happening is the large inrush of motor in the fan (5-7x nominal) is creating a high di/dt (rate of change of current) which is parasitically coupling to ground. since some of the current is going to ground, instead of returning to the source, it triggers the GFCI as a differential fault. if this is the problem, then solution is to buy a fan with an advanced motor drive inside (variable speed) and hope it comes with electronic protection against inrush. or maybe you could just coil up some of the source wire to create an inductance.. what do you think?

as for common mode trips, easiest solution here is to get some high-mue torroidal cores and just run the power wires through it. the black & the white through the donought center of the core. the common mode flux will circulate in the core.

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Old 06-28-2010, 12:35 PM   #36
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Quote:
Originally Posted by Knucklez View Post
where dose 1.43 come from?
UL 943, which probably used Dalziel's research. This formula is also in the online manual for Ideal's house wiring tester/analyzer, 61-165 or 65-165. It plots out as a straight line on log-log paper and I guess they used a best fit routine to match the data. The curve is a maximum.

Like a circuit breaker's trip curve is designed to prevent wire from reaching excessive temperatures this curve is designed to protect most people from injury or death. As I recall, Dalziel had trouble getting reliable data on kids because instead of reporting their discomfort level they would cry.

I guess a variable speed motor may help, if the speed control doesn't cause additional transients.

Last edited by Yoyizit; 06-28-2010 at 08:03 PM.
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