So having had one of these, and the consequent nasty mess it left, it strikes me that it should be really simple to spot (and since this is a Really Bad Thing it probably should alert me that I need to get it fixed pronto.
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This is a good idea and should definitely be easy to detect with the inputs Sense has available.
Also, to be clear, the OP is talking about a compromised neutral from the home service entrance to the utility transformer MGN, also referred to as an âopen neutralâ or âdirty neutralâ.
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Thanks for the clarification. There are various kinds of âopen neutralsâ. Sense could help detect the one you describe, but probably wouldnât detect an âopen neutralâ out on a multi-wire branch circuit. Also somewhat dangerous, but mostly for your 120V devices.
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+1 to vote for this. Trivial to detect.
An open neutral on the main feed from the utility will at best be expensive (fried devices), and at worst end up in loss of life and property.
They are seriously no joke. Sense is in a fantastic position to help identify these conditions rapidly.
I realize that this wonât get a lot of votes since it is relatively rare and most folks donât even know what it is, but I really hope Sense will consider making it a feature.
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+1000 - We lost the neutral from our utility feed from the pedestal to house early July of this year. The wire cooked underground. Seriously no fun, but Duke Energy was quick to respond. After replacing the line to my house from pedestal, the line from transformer to pedestal cooked that same day.
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You have my upvote for this feature request. It should be fairly easy to implement and should trigger a notification on the mobile app. Detection would be by a variation greater than a certain percentage or a certain number of volts between the voltage of the two lines.
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I would vote for this as well. Seems fairly easy to implement as sense already monitors the voltage on both legs of the panel.
I would have thought this was pretty uncommon, but am beginning to believe it happens more often than I would have expected.
It happened to my sister a few years ago, wire disconnected from the transformer at the pole in the middle of the night and blew out almost everything in her house.
Just yesterday a coworker asked me to help diagnose an electrical issue at his house. The lights were going crazy and he thought it was something with his solar system as he was getting high voltage. After telling him to turn of the solar he was still seeing the issue. I had him measure the voltages at his dryer plug and then contact the power company to let them know he had a bad neutral.
The power company confirmed this and since his service is buried installed a split phase transformer, at his house to solve the issue until they could fix his service. The fact they had this readily available indicates the problem occurs somewhat commonly.
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I agree with all the other user comments. This seems to be an easy software upgrade to make. It is one of those features that you hope you never receive an âalert notificationâ; but if you do, then you could take steps to mitigate damages.
I also encourage SENSE to graph the voltages for each leg so that we have the history recorded (not just the instantaneous readings located on the âSense Monitorâ page). I would like to know when we are having a âbrown-outâ or an âover-voltageâ spike.
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Up vote on the main topic as well as the historical voltage graph in order to keep the Utility honest.
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Can someone explain what a floating neutral is, how it happens, and how common it is?
At the utility transformer, the input is (typically, something like) 27,000 volts. That is, volts âabove groundâ. It produces two âphasesâ, of opposite signs, based on the direction that the wires take around the transformer core. There is one set in the + direction, and one in the - direction.
Both of those output voltages are âabove groundâ. The high-voltage power system is âgroundedâ in thousands of places, at each transformer. So the +120 and -120 voltages are relative to that common ground.
There are 3 wires from the transformer to your house. +120, -120, and âneutralâ. The neutral is connected to the âgroundâ of the high-voltage system, at that transformer.
If that âneutralâ wire is loose, disconnected, or has any other mechanical problem, it is called âloose neutralâ. It is loose in the sense that the voltage is not zero â it can âfloatâ to other voltages, depending on how much power is being used in the +120 and -120 circuits at that moment.
The difference between the +120 and the -120 will still be 240 volts. But, your house doesnât know where the â0â should be. This can result in some 120-volt circuits getting 160 volts, while other 120-volt circuits get only 80 volts. The total will be 240. But it can be split anywhere in the middle. As one consequence, your plumbing or conduits can be energized.
The too-high or too-low voltages, can damage some of your 120-volt appliances. The best that can happen is that they wonât work right, or will turn themselves off. At worst, your televisions and computers might need to be replaced, or one of them might even start a fire.
How common is this? It âshouldâ never happen. When it does happen, the power-company will dispatch a crew (immediately) to correct the problem. It is a big safety issue â so they give it high priority.
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Great description. So a clear distinguishing sign of a âweak neutralâ from the transformer would be mains voltages that are significantly out of balance, from one another ? Seems like that is a check that one could also do manually by looking at mains voltages ? Thatâs also a check that probably should be done by Sense in the setup phase, if it isnât done already, as it could cause wildly erroneous power results.
Or are there cases where an earth ground to neutral on in the breaker box, or a earth grounded neutral coming in from the backfeed might mask the missing neutral connection to the transformer ?
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+1 for Sense diagnosing this issue, if present
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Is/was this method of installation common? I have a newer home (built in 2008) and my neutral and ground buses are bonded in my panel and connected to an earth ground (ground rod). I suppose I could still get a floating neutral, but it would be in my panel and be my problem to fix, not the utilityâs.
All US electrical domestic installations join neutral and ground at the main breaker box. What weâre talking about is at the utility transformer - where the center tap is connected to ground. If that connection comes loose - and it happens quite a lot - then the L1 and L2 lines are âfloatingâ - they do not have a reference to ground, and the voltage between (say) L1 and neutral/ground is indeterminate - it depends mostly on the impedance of the âstuffâ you have connected between L2 and ground, and L1 and ground.
Hope this helps
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While it is one the Labs section of Sense (some disclaimers required), Fault Detection / Power Quality check will surface these kinds of issues.
That and the Fault Detection: Floating Neutral Check
Upvoted but to modify the original request for sense to monitor for all feed wire problems (Power feed and neutral). I had a connection go bad in my meter base which caused crazy power flickering. I was able to use sense to help identify the problem. Sense should have been able to see that and it could have come up and said "Sense has detected abnormal voltage levels, inspect any newly installed electrical items or check for wiring problems "
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Looking at some old notes, I saw this one about loose neutrals⌠There was a loose neutral at the power company transformer on the pole behind my house, when I wrote the previous reply in 2018. That was five (5) years ago. It was not disconnected, just high-resistance. When it was wet (from rain), it worked ok. When it was dry (after a few days without rain), it was not ok.
I reported that problem to the power company in 2018. They just said it wasnât a problem. Didnât even send a lineman or tech to look at it on site. I reported it to them periodically after that. In August of 2023, FIVE YEARS after I first reported the problem to the power company, they sent a tech to look at it, on a rainy day. A few days later, on Sep 1, they sent a line crew on a dry day. They changed the wire, finally.
Here is a screen shot of the power-quality graph, taken on a typical dry day. This was typical for most of five years. Note that one âlineâ goes well above the middle, and the other moves in a mirror image of that movement, during the peak-use periods.
During that entire five years, I never did get a âLoose Neutralâ alert from Sense. This neutral was not completely disconnected, ever. It just had high resistance, and the connection was frequently arcing. Because neutral is connected to ground at each house, even a disconnected (at the transformer) neutral would not have infinite resistance.
At the end, the problem was corrected. It just took a lot longer than it should have. When the lineman finally climbed the pole to look at it, there were two problems: a loose screw in the clamp holding the neutral wire; and an undersized (4g) neutral wire.
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Yes. When the center tap is loose at the transformer, the voltages on L1/L2 depend on the âstuffâ that is connected L1-ground and L2-ground. The thing to realize is, that âstuffâ is not just your own house. That âstuffâ is all of the (typically 8 or 10) houses that are connected to that transformer.
The law of large numbers applies. The variance of 10 samples will be smaller than the variance of 1 sample. And all 10 of those houses have their own âgroundâ connections, so the connection at the transformer is not the only one. That makes is hard to âseeâ the transformer connection, electrically.
It took me more than 5 years to convince my power company (FPL) to have a linesman climb that pole to look at that connection. When a linesman finally did climb that pole to look at that connection, a few weeks ago (Sep 1, 2023), he put a wrench on the clamp that held the neutral wire at the transformer, and said âFuck, Thatâs loseâ.
One hour later, my power was (finally) clean.