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Discussion Starter · #1 ·
I was performing some work yesterday on my house, and noticed when the breaker in the main panel feeding my sub panel was off, and the neutral was removed from the subpanel, all connections went hot. L1 to L2 was 140/150vac, neutral to L1 (or L2) was 120+vac, even the neutral from the main panel to the sub panel's neutral bus bar had potential (I forget how much).

Am I correct in assuming this means some circuit downstream from the subpanel is backfeeding? And most likely, there's a shared neutral somewhere, at a device which is being fed from a hot wire on a different breaker from the main panel but the neutral from the sub panel?

I've attached pictures of the main panel and sub panel. The voltage is present when I remove the "Neutral from Main" wire on the subpanel. With it in place, the panel is dead, with no voltage anywhere.
 

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Turn off all the breakers in the sub panel and see what voltage readings you get. If there is a back feed that should kill it. If you were using a high impedance digital meter it could also have been a phantom voltage.
 

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Why are you removing the neutral?
 
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Discussion Starter · #4 ·
Turn off all the breakers in the sub panel and see what voltage readings you get. If there is a back feed that should kill it. If you were using a high impedance digital meter it could also have been a phantom voltage.

Makes sense. I could turn them all off, and if the voltage goes away, switch them on, one at a time, to identify the circuit which is causing the issue (shared neutral maybe?).


The meter is a "Commercial Electric" HDM350 ... but when I reconnected the neutral, it did spark.
 

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The spark you get when putting the neutral back on its lug is a result of the fact that you are sharing a POCO transformer with your neighbor/neighbors and your ground system carries part of their neutral current.

As for the strange voltages, they're probably phantom readings unless you happen to be stealing power with a meter bypass connection. :biggrin2:
 

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Discussion Starter · #7 ·
The spark you get when putting the neutral back on its lug is a result of the fact that you are sharing a POCO transformer with your neighbor/neighbors and your ground system carries part of their neutral current.

As for the strage voltages, they're probably phantom readings unless you happen to be stealing power with a meter bypass connection. :biggrin2:
My transformer is dedicated for my house only, it's not shared.



Definitely don't have anything routing around the meter. Actually, the electric company was out last Friday and replaced my transformed and drop to the house. All part of trying to solve the flickering issues.



Here's a video demonstrating. Apologies, my wife didn't get the camera angle to see the meter on the 1st few readings.


 

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The spark you get when putting the neutral back on its lug is a result of the fact that you are sharing a POCO transformer with your neighbor/neighbors and your ground system carries part of their neutral current.
This should not be an issue for a sub panel neutral. I do not see where the OP states he is getting a spark.

I still think it is phantom voltage. I can not think of a situation where removing a neutral would induce voltage that was not there previously.
 

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Discussion Starter · #9 ·
This should not be an issue for a sub panel neutral. I do not see where the OP states he is getting a spark.

I still think it is phantom voltage. I can not think of a situation where removing a neutral would induce voltage that was not there previously.

It definitely sparks when I reconnect the neutral in the subpanel. It's actually what made me check for voltage.



Of course, I checked everything after throwing the breaker and before working on it. Luckily, when I disconnected the neutral to check it's condition, I touched it back to the lug and it sparked, before I touched anything else.


Would phantom voltage be 146vac?
 

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Could be that the POCO ground is defective. Could be your main panel isn't bonded to neutral. Very odd about that voltage though??

I think you need to get the POCO involved.
 

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Discussion Starter · #12 ·
Spark is not phantom voltage.

Gotcha. I wonder if the hot from another breaker in the main panel is feeding a device which has its neutral coming back to the subpanel, or tied to both the main neurtal bar and the sub panel bar?



That could cause this, correct?
 

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Discussion Starter · #13 ·
Could be that the POCO ground is defective.

You mean the earth ground at the pole? I took a quick look at it yesterday, there's a the wire coming down the pole from the transfomer, then bonds to a stake n the ground.



I suppose I could check for continuity between that and the neutral in my main panel?
 

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I'd get the POCO involved... there's no way you should be getting that high voltage reading. They may not have tied their neutral down or else they don't have a good ground connection. You mentioned that they worked on the system recently.
 

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Discussion Starter · #15 ·
I'd get the POCO involved... there's no way you should be getting that high voltage reading. They may not have tied their neutral down or else they don't have a good ground connection. You mentioned that they worked on the system recently.

They're actually coming back today to attach a logger to the mains. I'm pretty sure I'm getting fluctuations on the feed, but they insist I'm not (based on their grid monitoring). But if like you say, there's an issue with the ground at my pole, then their monitors wouldn't pick that up.



I can show the guy this video when he gets here and see what he thinks.



I just figured I had internal house wiring issue causing this, like the shared neutral situation. Wouldn't that do it? If a breaker on the main panel was on, power flows over the hot, to a device in the house .. and if that device's neutral is coming back to the subpanel ... then if I disconnected the neutral, I can see how I'd get potential there.



Is my thinking off?
 

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The spark at the neutral tends to indicate that the neutral in that subpanel is probably connected to ground somewhere in your system. It could be at the range or dryer if they are using the old 3 wire cords. Perhaps your water pipe connection to the ground electrode conductor isn't connected??

Lots of possibilities to check here.
 

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Discussion Starter · #17 ·
The spark at the neutral tends to indicate that the neutral in that subpanel is probably connected to ground somewhere in your system. It could be at the range or dryer if they are using the old 3 wire cords. Perhaps your water pipe connection to the ground electrode conductor isn't connected??

Lots of possibilities to check here.

Hmm, interesting thoughts. The subpanel only has 120v though, so no 240v there. If the dryer was wired this way, and running off of a 240 breaker in the main panel, would it still cause this? (house is 100% electric BTW, no gas)



As for the water pipe connection ... I actually looked over my main panel, and I don't see a main grounding connection anywhere. Would it be in the meter box maybe?


House was built in 1998.
 

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I just figured I had internal house wiring issue causing this, like the shared neutral situation. Wouldn't that do it? If a breaker on the main panel was on, power flows over the hot, to a device in the house .. and if that device's neutral is coming back to the subpanel ... then if I disconnected the neutral, I can see how I'd get potential there.

Is my thinking off?
I can see how that could happen if the main panel neutral wasn't in good shape and need the sub panel neutral connected so it could backfeed through the range or dryer connection to ground.

That still doesn't explain that high voltage reading.

The light flickering problem figures in here also... a faulty neutral connection at your pole or on in to the main is suspect.

The neutral system seems to be relying too much on the ground system.
 

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Discussion Starter · #19 ·
I can see how that could happen if the main panel neutral wasn't in good shape and need the sub panel neutral connected so it could backfeed through the range or dryer connection to ground.

That still doesn't explain that high voltage reading.

The light flickering problem figures in here also... a faulty neutral connection at your pole or on in to the main is suspect.

The neutral system seems to be relying too much on the ground system.

The dryer, range, HVAC, etc .. systems are all fed by breakers in the main panel. So even if they were wired incorrectly at the outlets, wouldn't it keep the issue off of the subpanel?



Your comments did get me thinking though.



What if the bonding strap in the main panel between the two grounded/grounding bars was weak?. Current returning to the main panels left side bar wouldn't be able to cross over the bonding strap to the transformer's neutral .... so it would look for another way, right?



The subpanel's neutral connection comes off the left bar in the main panel, and the subpanel's grounding connection comes off the right. But since the grounding and grounded bars in the subpanel are not bonded, it still shouldn't cause this (I don't think...).


It's looking like my best bet may be to call in an electrician to troubleshoot this. I have a good understanding of electricity, but trying to trace down a shared neutral, or illegal ground-to-neutral connection at a device, may be beyond my skillset.
 

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You are correct, it would take a neutral to ground connection in the sub panel or in some junction or load for it to offer an assist to a faulty neutral from the pole to the main. Double trouble is harder to troubleshoot.

I do consider the neutral to be erratic somewhere from your meter pole on to the main.
 
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