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Old 10-21-2011, 04:07 PM   #76
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GFCI trips at the same time


First I want to thank you westom for your knowledge and input. I have learned quite a bit from everyone on this forum.

Now to my questions:

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Leakage that may be traceable to, for example, a damaged line filter inside some appliance due to a previous anomaly.
Just to confirm, the leakage would have to be from an appliance on the same circuit(breaker)?

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One can spend $27 for that circuit tester to locate the defect. Or do same for a few dollars with a plug and a few Radio Shacks resistors. Neither is dangerous - obviously - because a GFCI powers everything.
To me, the Radio Shack route is dangerous because I am not an electrician and have not been provided DETAILED instructions on how to create this device. Since basic tasks as how the resistors should be wired (in parallel or series) were not explained, I'm not comfortable that I have everything I need to make this device.

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Old 10-21-2011, 04:12 PM   #77
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GFCI trips at the same time


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Cool. That's exactly what I (we) expected. I assume the POCO is going to do something about it? If switching in the capacitor bank is causing a voltage transient sufficient to trigger surge protection and bother UPSs, then something's not quite right with their cap bank.
The POCO made no effort to do anything about it. He claimed that the capacitor bank is operating as designed. He simply thought that I had really good surge protectors and told me to remove the GFCI and replace it with a regular outlet.

The POCO claimed that the capacitor bank should only be causing a voltage transient of 1-2 volts. I recently had a control board go out in my furnace (only 4 years old)... I wonder if the capacitor bank is responsible for that.

Last edited by ATJaguarX; 10-21-2011 at 04:25 PM.
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Old 10-21-2011, 04:46 PM   #78
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GFCI trips at the same time


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To me, the Radio Shack route is dangerous because I am not an electrician and have not been provided DETAILED instructions on how to create this device.

Long before GFCIs existed, a GFCI designer demonstrated it to the press. I found this test so unacceptable that I will never forget it. He had his daughter in a bathtub. Then he threw a powered appliance into that bathtub. She was unharmed. He proved his point. But

GFCI means you could be holding those resistors when powered. And never be harmed. However, like the girl in a tub, I do not recommend it. I am always that cautious.

Connect three 100 Kohm resistors in parallel from the hot (typically tinted copper colored) wire connection to the safety ground (typically tinted green) wire connection. Reassemble that plug. Plug it into one of two GFCI outlets. That should make the GFCI more sensitive to any partially leaking appliance. IOW, a few milliamps leaking inside an appliance would trip a GFCI that already has 2+ ma leaking through that test plug.

Now, this test has no danger and multiple layers of safety. But it always remains a thrill to connect something for the first time. Part of why I so enjoy doing things. And why I always stand back when even connecting anything I believe should never fail. Fear even of the impossible is exciting. Oh. And Happy early Halloween.

I went back and setup a custom GFCI tester I had built. It is adjustable. I set it for a leakage of 4.5 ma. Could not get noise from any adjacent appliance (vacuum, fluorescent lamp, etc) to trip it. Noise did trip that GFCI when I setup a leakage of 4.8 ma.

Now the math. From ohms law where voltage equals current times resistance. Three 100 Kohm resistors in parallel is 33K. 120 volts divided by 33K is the leakage current. About 3.6 milliamps.

If using two resistors, 120 volts divided by 50 Kohms (two resistors in parallel) resistance is 2.4 milliamps leaking from hot to safety ground. Neither should cause the GFCI to trip.

If I remember, your GFCI is in a breaker box. Therefore leakage may also be in wires inside the wall. Another viable suspect; but only after the test is done.

Since you now have a another relevant item (switching capacitors), then you might try the test plug overnight with two resistors and later with three resistors. With the GFCI not powering anything else. To provide further insight into noise from that capacitor bank.

Surge protectors ignore voltages below 330 volts. That let-through voltage is written on each box. Capacitor bank would never create 330 volts on 120 volt service. (Other electrical parameters may be relelvant - just not here and not yet.)

And finally, curiosity. Who is the GFCI manufacturer? There might be information unique to his design.
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Old 10-21-2011, 04:48 PM   #79
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GFCI trips at the same time


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The POCO made no effort to do anything about it. He claimed that the capacitor bank is operating as designed. He simply thought that I had really good surge protectors and told me to remove the GFCI and replace it with a regular outlet.

The POCO claimed that the capacitor bank should only be causing a voltage transient of 1-2 volts. I recently had a control board go out in my furnace (only 4 years old)... I wonder if the capacitor bank is responsible for that.
That's not good. If your UPS detected the event, it's not a 1-2V transient. That wouldn't cause the surge protection/GFCI issue, either. I think you should request that they do power quality monitoring. Most POCOs have portable power quality monitors they can install temporarily to record issues like this and figure out what's going on. Does your UPS log any quantitative data about power quality events, like the line voltage?
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Old 10-21-2011, 08:42 PM   #80
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GFCI trips at the same time


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That's not good. If your UPS detected the event, it's not a 1-2V transient. That wouldn't cause the surge protection/GFCI issue, either.
My UPS is currently set at the "High Sensitivity" setting. It switches to battery power under 88Vac or over 136Vac. To me... this is telling me that it picked up at least 136Vac.

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I think you should request that they do power quality monitoring. Most POCOs have portable power quality monitors they can install temporarily to record issues like this and figure out what's going on.
I'll call the POCO back and request that they install a power quality monitor.

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Does your UPS log any quantitative data about power quality events, like the line voltage?
I don't believe my UPS logs any real data. It does tell me the current Vac (which usually swings between 121 and 123). I'll have to look to see how I can get any more data out of the logs (if I can).

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If I remember, your GFCI is in a breaker box. Therefore leakage may also be in wires inside the wall. Another viable suspect; but only after the test is done.
My GFCI is attached to the side of the breaker box and is the only outlet on the circuit/breaker.

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Originally Posted by westom View Post
Since you now have a another relevant item (switching capacitors), then you might try the test plug overnight with two resistors and later with three resistors. With the GFCI not powering anything else. To provide further insight into noise from that capacitor bank.
Thank you for the idea... I'll try that too!

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Surge protectors ignore voltages below 330 volts. That let-through voltage is written on each box. Capacitor bank would never create 330 volts on 120 volt service.
My UPS kicks in at 136Vac.

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And finally, curiosity. Who is the GFCI manufacturer? There might be information unique to his design.
Pass & Seymour 2095-WCC10

Last edited by ATJaguarX; 10-22-2011 at 01:22 AM.
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Old 10-21-2011, 08:52 PM   #81
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GFCI trips at the same time


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One can spend $27 for that circuit tester to locate the defect. Or do same for a few dollars with a plug and a few Radio Shacks resistors. Neither is dangerous - obviously - because a GFCI powers everything.
I actually picked up this circuit tester for less then $10. If it doesn't fill the need, I'll build the one that you described.

Thanks for explaining in detail on how to build the tester, how to use it and what to expect. It has helped me better understand the issue and how to troubleshoot it.
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Old 10-22-2011, 04:58 PM   #82
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GFCI trips at the same time


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Do the experiment.

Buy a plug from Lowes. And two 100 Kohm (1/4 or 1/2 watt) resistors from Radio Shack (part number 271-1131). Connect two (or three) 100 Kohm resistors from the plug's hot prong to its safety ground prong. When that plug is connected to the GFCI circuit, then leakage will be about 2 (or 3) milliamps. Not enough to trip a GFCI. But maybe enough to trip that GFCI when a defective appliance (or defective wire in the wall) is also powered by that circuit.
I did the experiment with (3) 100 Kohm resistors. No appliances tripped the GFCI.
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Old 10-22-2011, 06:24 PM   #83
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GFCI trips at the same time


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I did the experiment with (3) 100 Kohm resistors. No appliances tripped the GFCI.
Ok. Now use the same tester plug on the GFCI with nothing else connected. Let's see if the capacitor bank switching causes GFCI tripping through that 3+ ma leakage.


At this time of year, electric usage is particularly low at night. The grid has a problem. Too many generators and not enough load. So they disconnect those capacitors to make the grid less efficient. Because generators cannot be turned off overnight.

Your capacitor may be switching only on weekday mornings as load increases significantly. But a more constant weekend load may mean those same capacitors remain unswitched. This test should continue even into the weekdays. Or unless test plug leakage causes a trip during the weekend.
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Old 10-22-2011, 09:49 PM   #84
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GFCI trips at the same time


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Your capacitor may be switching only on weekday mornings as load increases significantly. But a more constant weekend load may mean those same capacitors remain unswitched.
I experienced a trip last Sunday morning. We'll try tomorrow morning and see what happens.
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Old 10-22-2011, 10:23 PM   #85
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GFCI trips at the same time


Here is a picture of my device
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GFCI trips at the same time-p1010059.jpg  

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