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Old 09-17-2010, 01:47 PM   #1
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UPS tripping 20A GFCI in basement


Hey folks,

I am trying to figure out why one of my GFCI breakers keeps tripping.

It is a dedicated circuit (12/2) running approximately 50 feet to a demarc on the wall, where it serves a double duplex receptacle in a metal box, through a 4' stub of EMT. I have a large (1500VA) UPS plugged into this for my networking & computer gear.

Occasionally (once or twice a month), the GFCI breaker will trip. I am using 3.5A on the circuit so I doubt it is an overcurrent (no evidence that I've found).

I have replaced both receptacles, the entire run of 12/2, and the GFCI breaker. It still trips. I've even swapped in a different UPS, and it does the same thing.

If I run a heavy-duty extension cord to *another* GFCI-protected circuit, it does *not* trip.

Normally, I'd say it's a weak or poorly-calibrated GFCI, but swapping out the breaker seems to eliminate that.

The grounding is good, no nicked conductors, no wet conditions, all new work. The part that boggles me is that I've literally swapped out *everything* but the networking and computer gear, and it does the same thing. Until it's run to a different circuit - then it's fine.

?

Benny

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Old 09-17-2010, 03:40 PM   #2
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UPS tripping 20A GFCI in basement


Harmonics from the UPS.

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Old 09-17-2010, 05:09 PM   #3
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UPS tripping 20A GFCI in basement


I can certainly believe that... But why just one circuit? Why not the other one, too?

Is my only solution to .. gasp .. run this thing off an extension cord?

Thank you!

Benny
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Old 09-17-2010, 05:25 PM   #4
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UPS tripping 20A GFCI in basement


Is that part of the basement finished? If it is then the GFCI is not required.
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Old 09-17-2010, 05:28 PM   #5
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UPS tripping 20A GFCI in basement


Quote:
Originally Posted by bensec01 View Post
Hey folks,

I am trying to figure out why one of my GFCI breakers keeps tripping.

It is a dedicated circuit (12/2) running approximately 50 feet to a demarc on the wall, where it serves a double duplex receptacle in a metal box, through a 4' stub of EMT. I have a large (1500VA) UPS plugged into this for my networking & computer gear.

Occasionally (once or twice a month), the GFCI breaker will trip. I am using 3.5A on the circuit so I doubt it is an overcurrent (no evidence that I've found).

I have replaced both receptacles, the entire run of 12/2, and the GFCI breaker. It still trips. I've even swapped in a different UPS, and it does the same thing.

If I run a heavy-duty extension cord to *another* GFCI-protected circuit, it does *not* trip.

Normally, I'd say it's a weak or poorly-calibrated GFCI, but swapping out the breaker seems to eliminate that.

The grounding is good, no nicked conductors, no wet conditions, all new work. The part that boggles me is that I've literally swapped out *everything* but the networking and computer gear, and it does the same thing. Until it's run to a different circuit - then it's fine.

?

Benny
As a test, try using that same extension cord and plug it into the circuit where you are having problems.
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Old 09-17-2010, 05:35 PM   #6
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UPS tripping 20A GFCI in basement


Unfortunately, no, the basement is not finished.

I'll try moving the extension cord... It happens quite rarely, so if I do switch it over it might take several days/weeks for it to trip again.

Thanks everyone! I'll switch it this weekend, but would appreciate any additional thoughts...

Benny
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Old 09-17-2010, 06:27 PM   #7
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UPS tripping 20A GFCI in basement


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Unfortunately, no, the basement is not finished.

I'll try moving the extension cord... It happens quite rarely, so if I do switch it over it might take several days/weeks for it to trip again.

Thanks everyone! I'll switch it this weekend, but would appreciate any additional thoughts...

Benny
The extension cord may be providing some filtering. An extension cord has inductance and interwire capacitance so if the tripping is related to harmonics as previously mentioned the cord may be filtering them or at least attenuating them.
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Old 09-17-2010, 06:39 PM   #8
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UPS tripping 20A GFCI in basement


Does it only happen when UPS makes a transfer? i.e. during once every 7/14 day testing, or manually initiated testing?
IT equipment always have hot to ground capacitor filter and these things add up and contribute to bleed current seen as "leakage current" seen by the GFCI.
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Old 09-17-2010, 07:03 PM   #9
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UPS tripping 20A GFCI in basement


a7ecorsair: Ah, that would make sense... I'm very very rusty on my EE stuff, but that very well could be the case.

HVAC_NW: Nope. It appears to be random. My UPS units should kick off a self-test every two weeks, and it is not timed like that. Also, I have checked the event logs and I'm not able to correlate the GFCI trips with any sort of power event (I have multiple UPS units in the house, and none of them indicated any sort of problem).

Thanks everyone!
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Old 09-17-2010, 08:31 PM   #10
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UPS tripping 20A GFCI in basement


Benny, Welcome to the Forum
GFCI’s protect against Fault currents above 5mA.

Unfortunately the word Fault conveys the massage that any leakage current is bad and has to be eliminated. This is NOT possible in real circuits and leakage current is actually built into the input of some devices like in a UPS input line PI filter. Leakage current on very early Microwave ovens was so large that when kitchen GFCI’s were first introduced that they would trip when connected to a GFCI.

The leakage current on your large 1500VA UPS is less than 5mA but it is not zero. There is also some leakage current on other devices plugged into your primary GFCI circuit. The background leakage for those devices added to your UPS is still less than the 5mA trip point until something else occurs on that circuit such as a motor turning on.

If you tried using the second GFCI circuit over a period of at least a month
Quote:
Occasionally (once or twice a month)
Then that circuit has less background leakage than your primary GFCI ckt.

To get rid of the occasional trip problem you can
1) Plug the UPS in a Non-GFCI circuit
2) Use the alternate GFCI circuit since this does not cause the problem
3) Use an Isolation Filter on the UPS AC input

Since your UPS input is running at 3.5 Amps, You may get by with 500W Xfmr.

http://www.mcmelectronics.com/produc...S500-/28-10160
.
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Last edited by PaliBob; 09-18-2010 at 08:52 PM. Reason: sp
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Old 09-17-2010, 08:45 PM   #11
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UPS tripping 20A GFCI in basement


Thanks for the explanation, Bob... That makes several missing pieces fall into place for me.

Ouch, isolation transformers are pricey. While I'm running at 3.5A now, I don't want to limit myself to only having that capacity on my dedicated demarc circuit. They get a lot pricier than I can afford right now, for the higher capacity.

Now, I don't have my NEC book handy, but aren't single receptacle dedicated circuits in normally GFCI-requiring areas (like my unfinished basement) exempt from the GFCI requirement? If I'm remembering correctly, I could swap out the double duplex receptacles and install a single (not duplex, think fridge receptacle).

Not that I like that solution either - GFCIs exist for a reason, and I'd rather have the protection.

Thoughts?
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Old 09-17-2010, 08:46 PM   #12
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UPS tripping 20A GFCI in basement


A while back I made a GFCI Tester to measure the GFCI leakage current down to 1mA.

GFCI Tester
.
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Old 09-18-2010, 01:30 AM   #13
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UPS tripping 20A GFCI in basement


Quote:
Originally Posted by PaliBob View Post
A while back I made a GFCI Tester to measure the GFCI leakage current down to 1mA.

GFCI Tester
.
That is pretty cool item you made and I have master GFCI tester so I can able adjust the level of current leakage

This is the item I used pretty often



It do pay itself more than once with few service call with bad GFCI devices.

Otherwise I will use the Wiggy soilnd tester that will trip the GFCI real quick.

Merci.
Marc
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Old 09-18-2010, 04:25 AM   #14
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UPS tripping 20A GFCI in basement


Benny, I do not know whether or not a single ckt outlet would be legal in your basement.
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Old 09-18-2010, 05:14 AM   #15
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UPS tripping 20A GFCI in basement


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Originally Posted by frenchelectrican View Post
....This is the item I used pretty often ......
Marc, I looked at that Greenlee tester before I came up with my own static design. I did not need the current pulse of the Greenlee because my Tester design loads max out at 4mA. When my tester is set to pull a 4mA fault current and the Green test light is still on, then I know the background ckt leakage is equal or less than 1 mA.

My design is used more to approximate the trip current margin on a GFCI ckt rather than checking whether on not the GFCI will trip. The only valid GFCI test acceptable by the GFCI manufacturers is their integral GFCI test button.

Here is a link for anyone interested in Marc's Greenlee Tester:

http://www.electricsuppliesonline.com/gr57gfandcit.html
&
http://65.36.183.19/greenlee/im/im1405.pdf
.

.
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Last edited by PaliBob; 09-18-2010 at 09:00 PM. Reason: clarification & bad Link
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