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Old 05-13-2021, 02:48 PM
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Default Troubleshooting Cross talk between GFCI circuit and another unrelated circuit

For those overachieving EE Troubleshooters who love a good challenge… This is currently stumping two electricians who've been to the house. I bought an older house (’77) with a pool (added 2012). The problem simply put is that there is some interaction between 2 non-related circuits in the house such that when the pool variable speed pump is set at or above a certain RPM speed, ~2200 RPM, it is tripping a GFCI outlet controlling my external house lights and outdoor receptacle which happens to have my deck string lights on it. The issue predates me adding the lights. There are two separate panels in the house and the outdoor GFCI is on one, and the pool on the other. The pool also has a sub-panel adjacent to the pool equipment with its own GFCI circuits which have never tripped. I figured this out thru lots of trial-and-error running around the house to understand why my outdoor lights kept getting shut off until I noticed the connection with the pump speed. At no time does the pool pump or pump related accessories lose any power when this happens.

The tripping GFCI is the one with the red test button on the left side panel in the first pic. The pool is the double switch in the right side panel, 2nd from the bottom on the left I think. The pump equipment sits on a platform about 8-10 feet from where the mainline enters the house. The pump appears to be dated 2016 so I suspect it’s not original. The panels are probably within 20 feet of the pool equipment too. If I select a lower pump speed it never trips. If I set a higher speed, it immediately trips. If I reset the breaker w/o changing speeds it immediately trips again. No noise or hesitation. If I set a speed very close to the threshold it will trip within minutes and immediately if I turn on one of the outdoor lights.

I’ve had two electricians here to look at it, and neither has been able to resolve the problem yet. Electrician #1 was onsite just before I figured out the relationship but he was aware of the outdoor light GFCI tripping issue and tried to investigate it too.

Electrician #2 was here to work on it, and was stumped. Electrician #1 (boss of #2) says it’s a voltage leak somewhere concerning the pump which is enough to trip the other panel's GFCI switch but we don’t know where its occurring. He thinks it may be the pump itself either in its control panel or motor such that when its rev'd up something is engaged which includes the fault. They temporarily swapped out the GFCI circuit breaker for a regular non-GFCI one, and sure enough everything stayed on. It also seems somewhat load related because it can be tripped either by hitting the pump switches for RPMs exceeding 2400, or by using the 2200 speed setting and then turning on one of the outdoor lights.

#2 checked for any lose grounds or neutrals and found none around the panels. #1 is coming back for a more intensive look soon. I'm already into this for about $500 in time w/o a fix in sight.
Current theory is that some shared common wire or ground is allowing feedback into the other GFCI circuit. I tried to cleanup the visible ground wires which appeared corroded in the hopes that might be the issue but no luck.
Also, it appears that the pool heater is sharing the same ground wire as the pump and it is on the same GFCI circuit on the sub panel. Per the pump’s manual the pump should be on its own unless it has a salt generator which this rig also has.

Thoughts?

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Last edited by joep; 05-13-2021 at 02:53 PM. Reason: formatting
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Old 05-13-2021, 04:00 PM
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I'd separate the ground wires for the pump and the heater as a first test.

Also, how close physically is the motor to any of the devices or lines on the tripping GFCI circuit (as in distance)?

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Old 05-13-2021, 04:16 PM
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The heater btw, is almost never used and typically off, although it is powered. The panels would be closer than the outdoor lights and outlet. The closest light is just above the outlet, say about 25-30 feet?
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'03 - boxster - Joy Toy
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-de-ambered
-Boxster Brey-Krause Roll Bar
'05 - 955s Gold - My Other / On Road / Off Road
-coolant pipe by pass 08/11
-heart & short soul block replaced @50k 01/12
-cardan shafted & replaced @125k 09/16

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I think I like the purple, it placates my lesbian side.
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Old 05-13-2021, 04:18 PM
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I will post in a bit later when can use a keyboard 20 years spent working on this stuff.
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Old 05-13-2021, 04:33 PM
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IANE, but strongly suspect interaction between the variable speed motor and the GFCI.

Have you tried another GFCI breaker, and/or another brand of breaker?
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Old 05-13-2021, 04:43 PM
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#2 did temporarily replace the GFCI breaker with a standard breaker and it never tripped (15-20mins). They said a replacement GFCI would be hard to come by atm due to covid supply issues, but I'm certainly willing to try it.
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'05 - 955s Gold - My Other / On Road / Off Road
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-heart & short soul block replaced @50k 01/12
-cardan shafted & replaced @125k 09/16

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I could feel my self-esteem rising, even while realizing how incorrect I was
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I think I like the purple, it placates my lesbian side.
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Old 05-13-2021, 05:32 PM
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1. Replace the GFIC with a new one. Whoever said an Eaton GFIC was hard to come by? Please take a picture of the panel data plate. Looks like common BR. Home Depot sells Eaton

2. All the rest. if the new device still trips the next step is to go through the Neutral system.

The sub panel should not have a bonded Neutral. Only place the neutral should be bonded is in the main panel. This includes mixing green grounds with the neutrals. It looks good in the pictures it you should check the the Neutral bar is not bonded to the box. Bonding is normally via one of the mount bolts but in small panel boxes it is done via a bolt that goes from the bar to the box so it is easy to remove for use as a sub.
Go through all the neutrals checking that they are clean and tight and right. Check this carefully in the main panel.

Agree that the motor speed control is likely back feeding enough non 60 hz noise to fool the GFIC into thinking there is an imbalance. have seen sort of similar issues in commercial non 3 phase. Short of checking with an O scope and MA meter or swapping out the motor controller perhaps put a big choke / ferrite on the GFICs sample Neutral.
You can also check the motor with an O scope to see how electrically noisy it is.

Forgot to add that if you disconnect the neutral at the GFIC it will act like a standard breaker.



Side note. The #8 bare copper wires are the Bonding system. It is there to connect everything conductive but not a conductor in the pool system to prevent any voltages. It should be in good shape but this is not where the back flow is coming from.
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Last edited by Vicegrip; 05-13-2021 at 07:23 PM.
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Old 05-14-2021, 03:43 PM
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Thanks for the suggestions everyone. Vicegrip looks like you guessed it!

So they came back today and tried some more testing. In the end what it appears to be is the GFCI breaker has become overly sensitive. #1 says its hard to really rule out everything and find the true ground fault, but what worked for now was a GFCI outlet by pass as pictured, and in the final pic they installed it.

The pump can work at any speed now and my other circuit is no longer impacted.

Rather than controlling my pool from an outlet I've asked them to get the replacement GFCI break and install that. In 5, 10, 20 years I dont want to have someone else needing to figure out why the pool won't work cus someone plugged in a hair drier.

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'03 - boxster - Joy Toy
-rolling convertible action
-de-ambered
-Boxster Brey-Krause Roll Bar
'05 - 955s Gold - My Other / On Road / Off Road
-coolant pipe by pass 08/11
-heart & short soul block replaced @50k 01/12
-cardan shafted & replaced @125k 09/16

Quote:
Originally Posted by BlackTalon View Post
I could feel my self-esteem rising, even while realizing how incorrect I was
Quote:
Originally Posted by Rick V View Post
I think I like the purple, it placates my lesbian side.
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  #9  
Old 05-14-2021, 04:57 PM
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Good news!

I wonder if there really is a ground fault. After the last storm and outage I had to replace a GFCI that failed, after having been occasionally flaky for a few years. All is well now. I think they're very sensitive, for good reason, and maybe there a fine line between very sensitive for real faults and intolerant.
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Old 05-14-2021, 10:01 PM
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VG did not 'guess it'
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