Seeing Big Difference Between Sense and Meter After First Month - What could be causing?

Finished 1 complete billing cycle, but there’s a huge disparity between my Sense measurements and the utility’s meter. 240 kWh measured in Sense, 443 kWh from the Utility’s meter. The weird thing is, the Sense has picked up all the big users (HVAC fan, fridge, etc.) and my heat/water heater is gas anyway.
I’m stumped what could possibly cause such a big discrepancy. Is it likely the meter itself is faulty?

Context: I’m in a house that was split into two condo units, but we each have separate meters and panels.


@yingc125, wow, that’s a significant difference. A few questions related to potential sources of differences.

  • Do you have a smart meter or does your utility rely on human meter readers ? Can you get a more detailed view of daily / hourly usage ?

  • Are you sure that Sense CTs are measuring exactly the same load as the meter ? Several users with initial big discrepancies missed a parallel circuit branch and subpanel that diverged after the meter, but before their main panel. Not as likely if Sense has truly found ever major device in your new unit - in other user cases the other branch powered things that the users had forgotten about - golf cart charger, what they thought to be non-functional heater, common laundry room.

  • Unlikely, but you don’t have 3-phase wiring vs standard US split phase service ? The only reason I mention that is that larger condos do employ 3-phase wiring.


@yingc125 The first thing to check on any “read” utility bill is whether the reading is ACTUAL (usually means a human got to the meter to read it) or ESTIMATED (some utilities won’t bother reading meters every bill cycle or things like snow or locked doors/gates can impede access). As @kevin1 implies, a smart meter avoids that issue.

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Our meter appears to not be a smart meter, it looks like a conventional one outside that a human would read.

I don’t have a sub panel, my unit is definitely not fancy enough for golf cart chargers or pools equipment. No common laundry room or anything.

I don’t believe it’s 3 phase wiring, our condo is just a larger single family house that was converted into 2 side by side units. For my main panel, it appears just one in, one out straight to my circuit breaker, and one going to the ground, unless I’m missing something. (maybe that one random green wire going between our main panels…?)

Oh interesting, no the bill says “actual”, but I don’t think it’s a smart meter by the looks of it.

@yingc125 , you should be able to post photos now. The system waits until you have a few confirmed non-SPAM postings before allowing pictures.

Thanks for photo - two questions.

  • Can you share a meter photo ?
  • Where is your Sense on installed ?

Are you #85 by chance? i’m noticing that it looks like there are two lines running out of the bottom of the panel where as #83 only has 1. I assume your Sense is installed in your panel which has all of the other breakers for your unit which I’m guessing is the dark grey wire that comes out of the bottom and routes back up. If you can, where does the grey conduit go off to the right?

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That’s true, the other one doesn’t have the light gray. That ones just goes down to, what I assume, is the ground wire that ends at the waste pipe on the ground. I wonder if that’s why there’s that one green wire that connects the two panels?

Here is a picture of my meter.

My sense is installed on my main circuit breaker.

3 thoughts:

  • The green wire that connect both breaker panels is most likely a fat earth ground wire.
  • The meter on the right (Itron) is smart but the Sangamo on the left looks ofd-school electromechanical (not smart). Non-smart meters have the added issue that the read dates might not correspond exactly with the billing dates, so number for a month could be off. Plus you can’t get daily, hourly or even every 15 min data from them (my utility gives me 15 min interval data, so much easier to check agains Sense).
  • @ben is right - breaker box for 85 looks like it is carrying an additional set of loads, not related to the the living quarters upstairs. Worth investigating what that bundle powers if you are 85.

So that light gray one leading out of #85 panel terminates to only this green line, connected to the water line. (which now makes sense, why that other wire connecting the two panels is also the same green.)

Also curious, should a ground wire connect to the water pipe…? If a fault occurs, would it only go to the ground, or potentially electrify all the water in the pipes in the house? (plumbing is all PEX, so it would only be the water I guess.)

So the only thing running through that second bundle is a ground wire ? Big sheath for something so small. That looks like your earth ground connection via the copper water pipe. The code requires a conductive pipe or rod that goes down 8 feet into the ground.

The green ground wire being connected to your water pipe is a typical grounding method. The amount of copper and buried metal pipe in a wet environment (read: conductive) is usually the best available interface “to the Earth”. The NEC (National Electric Code) allows for the ground wire to be bonded to a water pipe as long as there’s something like 10ft of buried pipe. The problem with using water pipe rather than a purpose-installed ground rod is that city water pipe these days can potentially have insulators to deliberately prevent conductivity and electrolysis that corrodes metal pipes. I think it’s probably rare though that grounding to water pipe is insufficient. It can really depend on soil types and moisture content. Take this info with a grain of salt though, a licensed electrician should have installed, verified/tested your grounding at some point.

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Yeah, that’s all that comes out of it. I’m thinking it’s a current leak somewhere else, maybe the insulator is worn but not completely gone that it would short circuit. Instead I’m probably losing (270w = ~2amps @ 120v?) assuming my 200 kWh/month is being used up continuously. Can Sense pick up leaking current under that “Other” group? If so, at least it would isolate the problem to either my circuit breaker or the wires running to it.
Booking time with my electrician.

To take this a step further. If you have a main breaker in your panel, turn it off. If you don’t (and in theory you won’t because your main is in the panel in the basement), turn off all the breakers on the panel where your Sense is installed including your Sense. Go outside and look at your meter. Is the horizontal disk spinning? If yes, power is being used elsewhere. If no, time to revisit your Sense installation. Check that the CT’s are actually on the correct cables and fully closed etc…


“Actual” means actual reading of the meter. Check last months bill, I’d guess it was estimated. A low estimate last month would cause a high actual this month.

We have NYSEG here, bills are estimated about every other month. Billing cycles run from 23-32 days with no consistency whatsoever. Have no way of knowing when they will actually read the meter.

Your best option will be to read the meter manually and compare it to billing cycle you set in Sense.

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Yes. However there must be a jumper across the meter (or across any threaded connection) to the side that passes through the wall. I noticed it appears you do not have one. A simple inexpensive fix. I believe the reasoning is if the meter ever needed to be replaced the person replacing it would become the jumper and electrocuted. Also if the threads ever became loose not only would you have a flood you are more likely to be electrocuted.

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Ah I never would’ve have thought of that, if the previous month’s was estimated. But I just checked, and it’s actual too, so I guess they don’t estimate here. And the readings do line up with what the meter says right now.
When the electrician finally comes, my first suspicion will be the wires running from the junction that our sump pump is connected to. they go to both by circuit breaker and the neighbors. And yet, there’s no recording of it on Sense. I wonder if they somehow wired it in upstream of the breakers main lines.
It seems like a stretch for my sump pump to use 200 KwH a month, since it only comes on after it rains, for a few seconds every several minutes. But maybe it got wired somehow into the neighbor’s circuit somehow, and it’s drawing almost 2 amps constantly at 120v, if my uninformed rough calculation is right.
Or you tell me if that sounds very unlikely, even in a scenario where our wires somehow got connected together.

From all your info thus far, yes it does seem unlikely the sump is using 200kWh/month.

I lean more toward the following possibilities:

  • Sense CTs not being ideally clamped around the wires. Check to see they are fully closed and that they aren’t pressing against the wires/panel when you close the panel up.

  • Your building services (outdoor lights?) and/or a neighbor’s circuit is feeding from your meter. Hard to tell how that might be wired. Where is the sump power feed and breaker for example? We seem to have determined that the ground is running to the sump pipe but where is the sump power? That is normally not wired to tenant’s meter though with only 2 meters evident it stands to reason that it’s powered by one of those metered feeds.

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