Is This a Floating Neutral ? What's Going On?

I’m curious, what does this look like to you all? A bad neutral? It started right as a kitchen renovation started, right as they started the demolition. The demolition didn’t get anywhere near the breaker panel.

It kept up. Sense only lets me post 5 at a time :upside_down_face:

I should note that around the 21st is when I noticed it. I did not get a notification from sense, but it’s when I heard the very quiet alarm from my Siemens FS140 ground reference monitoring feature. The problems are still ongoing according to sense, but the alarm hasn’t sounded for several days. It didn’t seem to go away after switching breakers off, either.

@test35965 ,
What are you seeing from the “Floating Neutral” part of the Sense Labs ?

ps: I think I’m going to start this up as a new topic.

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This is a floating neutral. The neutral should be balancing the voltage.

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This is not from the “Floating Neutral” detection in Sense.

It’s the kind of thing that would be useful for sense to detect!

Now I’m curious, why do y’all think it happened when the demolition started? Do you think it’s at the breaker or at an outlet? This is a 1983ish home. I’m not sure if I should check individual outlets, since I’ve heard about olden days use of shared neutrals, and many of these damn outlets were backstabbed. They were drunk when they built the house - I found beer cans from the 80s buried in the attic insulation :joy::man_facepalming:

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Now check this out. On the morning of the 28th, I tied some of the grounds together. The grounds I tied together are in outlets that were removed on like the 22nd pending the rest of the renovation. We left the house on that day, and also sense is a few days behind on this feature, so it’s too early to say what’s going on.


A couple thoughts.
First, my view is that that the Sense “Floating Neutral” detector should have caught this. I’m wondering if the the Labs “Floating Neutral” detector is experiencing some of the same operational issues and/or delays in being run that have occasionally beset the Power Quality checks. Since this is in the Labs area it is not guaranteed to be functional all the time, but I’m wondering if @JuliaAtSense or someone from the support team can check in on this. BTW - here’s how the Floating Neutral detector is supposed to work (yours is a no-brainer case in my mind):

As for what could have caused this to happen - I think you only get this phenomenon (voltage legs going in opposite directions) from a floating neutral at the breaker box or at the utility transformer, not from a broken neutral on a circuit (which can also be dangerous). Did the remodel any work inside your breaker box / distribution panel ? Or did the utility make any changes ? Sometimes the issue is just things like corrosion.

You can test for an open neutral on a specific outlet with one of these outlet testers.

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It appears to me that you do have a problem with your neutral cable.

Areas to check:

  1. Visibly check the ground connection from your breaker box to either the ground rod located outside your house or if it is connected to a metal plumbing pipe inside your home. Take pictures and post. You could have corrosion at the outside clamp. Or possibly the connection to your plumbing pipe ground was disturbed and is no longer connected. Either way, power everything off and clean up the connections with a wire brush. I had to clean and install a new ground clamp at my home. After installing, I got better voltage readings.

  2. Check the outside wires coming to your home. If you have an overhead line entering from a power pole, try to visually inspect the bare neutral ground wire. My brother had squirrels chew thru the aluminum bare neutral wire. It wasn’t completely eaten thru so his voltage readings were similar to yours. The power company had to completely replace his service drop to his house. It was free. If you have a ground transformer, have the power company check their equipment. Show them your graphs. It’s possible that their ground rod located at the transformer is not connected or has failed. Take pictures.

  3. If you have an external electrical shut-off and can access the inside of the breaker panel safely, then remove the panel door and check for a loose or ‘burned’ connection on the white/neutral cable. Also check the green ground wire. Take pictures. You need to check the main neutral connection point in the panel. The lugs might need to be tighten (to 25 ft-lbs). Wire is soft and will deform over a period of time. If you live in an area with saltwater corrosion, you should consider using an anti-corrosion grease on the wire and lugs (like NOALOX). If you don’t feel comfortable doing this yourself, then you should definitely contact a licensed electrician to provide a service check. The cost of hiring someone will save you money in less failed electrical appliances.

  4. Your ground wire from the breaker panel to the ground rod could be too small.

Keep us posted on your progress. Good luck!


Here’s the funny thing, yes, they did add a new circuit, but only several days after the first disruptions recorded by sense. Btw, sense here has been invaluable in diagnosing this. If it weren’t for sense, there might have been some nasty finger pointing. My best guess is that somehow the vibration and general movement from the demolition jiggled something loose somewhere.

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To my frustration, I don’t know where the exterior ground is. I will go on a safari when I’m back at the location! It’s a condo, and the three units were attached to have their meters ganged next to eachother. I do know that the power lines are not overhead, that’s clear to me :wink:

#3 is not super hard for me insofar as inspection is concerned. I’ve had that panel cover off a bunch of times and have a healthy respect for the dangers of electricity. I’m comfortable enough with live power to work around it, but not stupid enough to work on it. I hire pros when actual work needs to be done to the breaker panel.

A few years ago, I had it off to air seal the panel… If you’ve never checked before, you’d be shocked how much infiltration can come through panels if there’s no caulk in the penetrations to the attic or the building wall spaces.

Anyways, I did actually take the panel off so I could look at it with my little FLIR attachment for the camera for exactly this reason. Torque screwdrivers weren’t even around when this place was built, so I figured there’s a chance something might be loose and causing a high resistance connection. I didn’t see anything. Hence the confusion. Even more confusing, the ground reference monitor alarm was intermittent. I could actually tell because the Corsi Rosenthal boxes in the house would slow down intermittently. The intermittent part is what made this super frustrating when it first started. Nothing seemed to help!



I just wanted to check in here and say that I saw this thread. I can confirm that what @test35965 experienced was clearly a floating natural, and I’m glad it was caught. With that, the question goes, why didn’t it appear in the floating neutral section of the labs’ app?

What I can say is I’m working with some folks to figure out why. What @kevin1 already said is true; this is a lab’s feature and may not work all the time; it is also possible that based on the particular situation Sense didn’t pick it up.

This is helpful info to hear so we can work to improve and get us all looking a little harder at what to expect from floating neutral detection.



I experienced one floating neutral, 40 years ago, but they are memorable events. Mine was due the connections in the meter socket - my round meter had stabs that plugged into a socket. If my memory is correct, the underlying cause was corrosion between the copper stabs and aluminum lugs, but it has been 40 years. You can google that for better explanation.

From that experience, and as an EE, I suggest you focus on the neutral connection (the big bare wire at the service entrance, which ties to your neutral bar with all the white wires). Poor grounding can be a contributing (secondary) issue, but is not likely the root cause. When you lose your neutral connection, the two 120v legs, what we call the split phases, become a simple series circuit across 240v. You have lost the primary reference back to the center tap of the distribution transformer. Your ground wire can act as a secondary path for the neutral reference, but its resistance back to the transformer will vary and add to the confusion.

Without a solid neutral, the voltages on each leg float based on what is called a voltage divider principle. Perhaps when you turn lights on in Room A, you notice the lights actually get brighter in Room B. (My exact experience). That is because as you add loads on the Room A side, you actually give the electricity more paths to flow, and the parallel resistance goes down on that set of 120v legs. Due the voltage divider principle, the voltage on the Room B side will increase, such that the sum of Room A and Room B voltages always equal 240v. This phenomena will be present on all circuits common to the Room A side and all circuits common to the Room B leg

I cannot offer an explanation why this occurred when demolition started. Floating neutrals should always be the result of something amiss at the service entrance. I don’t want to think about more complicated scenarios where the house neutrals wired together somehow compensate and provide a neutral, that would be a sign to me of poor work and I just dont have enough understanding to run that one through my brain.

Hope this helps, others please chime in if you see something amiss in my explanation.

Terry B