Mini Split Dedicated Circuit - wrong setup?

Technical Questions
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#1

I have two Mitsubishi mini splits connected, but now think I wired them wrong. I followed the instructions, and pictures, here: https://sense.com/guides/dedicatedcircuit-advanced/ and made a loop for both of my second wires. When I turned the breakers back on for both units, I was getting ~50w for the fans in each. I thought everything was good. I show 12w of standby energy. My first clue of something being wrong is user @chrisd253 mentioning in this thread: What's new in: V33 (iOS/Android) V12 (Web): Dedicated Circuit Monitoring that his mini splits were using 13w and 19w in standby, but then settled down to just 5w. Mine use 12w always. Not out of the realm of possibility, but it got me thinking. I read in another thread that if both wires were doubled up, the energy usage would be double. So I went back to the installation guide and think what I did was to follow the 240/120 instructions with making a loop for one wire and feeding both through the clamps.

If I’m getting double the reading, my standby could be 6w, a lot closer to Chris’ mini splits and more in line with what I was thinking would be standby usage.

I have annotated a photo of my setup to show the path of both wires.

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The green arrows show the direction of voltage and path of the wires. I have basically talked myself into the idea that I set them up wrong. I tried testing it just now by turning on my AC, but instead of seeing the 900w increase in the power meter like I see over the summer, I only got a 50w spike. I’m guessing that is because it is 46° outside and the compressor is smart enough to know it only needed to use the fan to cool down inside.

Thoughts? Did I set it up wrong? Should I redo the wiring with just a single wire going through each CT? If I do rewire, do I need to change the setup within the Sense app, or just move out the extra wire and look to see what the app says?

Thank you!

#2

it’s kind of hard to see the one on the left but it looks like the one on the right has both wires going through it which would be wrong for the 240-volt setup. for some reason I didn’t take a picture of mine yesterday, I usually do, right after setting it up. I guess I was a little too eager to get it buttoned up, set up and head out on a bike ride.
It should have only one of the two wires going through the CT clamp., And it should only go through once.
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That’s how it would go if you have a balanced 240 volt circuit, in other words you have the two hot wires and a ground with no dedicated neutral return

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#3

If you put both wires of a single 240 circuit through the same probe/clamp, they will cancel eachother out because the are opposite polarity. You would only read the minor difference between the two lines.

“The clamp is put around one of the wires of the circuit to measure the current through that wire, if the clamp meter were put around both, the opposite currents would cancel each other out resulting in a reading of zero.”

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#4

Also if you put the two wires in fed through the clamp in opposite directions I believe it will read twice as much current, which may work if the probe wasn’t doing its own math. I know it is confusing. I think the way it is designed to work is to just clamp one leg on each 240 circuit and the sense unit will double the reading to assume the load is balanced between L1 and L2. This will free up a probe to monitor another circuit. This only works if the load is balanced. depending on what you select during setup. (2 devices on 240 = clamp one leg of each circuit). Some appliances that are 240 have unbalanced loads. Like a dryer may have the heating element on one leg L1 and the dryer motor on the other L2. This would require a set up of (select one device and 240V) and both probes for one appliance L1 and L2 because of the imbalance the sense cannot assume what the load is on other unclamped line so it has to actually measure both lines…

4 Likes
#5

I think there’s some confusion here. It’s hard to tell what’s going on in your images.

In short, there are three options to set up 240V circuits, each processed somewhat differently by Sense:

  1. Both CTs on both ungrounded leads from a 240V breaker. This method must be used if you’re attempting to monitor a single 240V circuit. See https://sense.com/guides/dedicatedcircuit-1load/.

  2. One CT around one ungrounded lead from a 240V breaker. This method should only be used if you’re monitoring a balanced 240V circuit, i.e., not connected to the neutral bus. See https://sense.com/guides/dedicatedcircuit-2loads/

  3. Both ungrounded leads through one CT, but one going through in reverse. This method should only be used if the load is unbalanced, i.e., connected to the neutral bus. If you use this method, the other CT must be used to monitor another 240V or 120V load. See https://sense.com/guides/dedicatedcircuit-advanced/

It’s not always obvious if a circuit is connected to neutral and wire color coding is not always the best way to judge. An electrician can confirm the correct setup type for you. It looks like you attempted to due the third option here? I’m no HVAC expert, but I don’t believe mini splits are commonly connected to neutral. I’m sure there are exceptions however and I’m sure someone will chime in here to correct me :slight_smile:

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#6

I did try option 3, and it worked in the sense that I’m getting readings. I think though that I over complicated the setup. I will take the loop out of my clamps and see what the readings are then. Will I need to resetup the detection, or since I selected two 240 devices from the start, do I just need to remove the wire and leave everything else? Thanks.

#7

I can only speak for my own setup but I have two Mitsubishi setups , one mini split, and one multi split. The two outside condensers have no neutral return. So as far as I know in my experience many splits don’t have a neutral

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#8

You will need to redo in-app setup, as the. math is totally different between the setup types. I’d expect that option 2 is what you want for these devices.

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#9

I just set up my Fujitsu mini-split on a dedicated circuit. It didn’t have a neutral, but I used both sensors on the single 240v circuit since I didn’t really have anything else worth breaking out. In my case I had to have the sun stickers facing away from the breaker on both conductors.

So far it’s doing a much better job of capturing the multiple variable speed motors!

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2 Likes
#10

I am here learning from this topic because my mini split is not being fully detected. My Sense detects a small signature watt draw but does not see the corresponding 2500+ watts that is always associated with that detection.

I am contemplating getting the secondary set of probes to monitor my HVAC usage.

Now I understand the three monitoring scenarios detailed above.

What I am contemplating, and PLEASE correct me if I am wrong, I was going to clamp both sides of the 220 breakers with each clamp… AND I was going to include both the MiniSplit AND the conventional Trane wreck ducted system to get the total heating/cooling regardless of which system I was running. So in my mind, I would have phase A of the mini, the Trane condenser, and the Trane air handler unit with (electric heat strip) in the same clamp (all wires running in the same direction through the clamp), and the same set up for phase B… of those same units. Yea or nay?

Oh, Hiya folks, this is my second post/topic and 5 weeks with energy monitor.

#11

I just did a test using a scope with Fluke i400s current clamp (transformer) and the answer is yes, it’ll work with complete accuracy if I understand your question correctly.

I used a variac to produce a 60Hz sine at 3 amps going through two loads; one 4 ohms, the other 2 ohms (power resistors). I then connected a single 12" wire from the variac hot that split into two 12" wires that fed the two power resistors. The current clamp read 3 amps on the single wire, 1 amp on the 4 ohm wire and 2 amps on the 2 ohm wire, care of Kirchhoff’s current law.

The thing I wasn’t sure about was sliding the current clamp from the single wire over the split and unto the two wires. I thought that the various positions of the two wires inside the eye of the clamp might cause a different reading - but it didn’t. I varied the wire positions as widely apart and closely together as possible and the reading remained locked at 3 amps. Pretty cool.

Thus you can run as many wires on the same phase through a single current clamp as you can fit in it and it’ll report the total without error. Just make sure the clamp is fully closed and the clamp’s contact surfaces are clean. Use wire ties on the cables to keep them from spreading apart enough to cause the clamp to open.

Finally, there is no reason to measure the second hot wire of a 240V dual pole breaker feeding a 240V device because the amperage (number of electrons passing a given point per second) is identical, just going back and forth 120 times a second. As @kevin1 has mentioned many times, if a neutral is involved (120V loads), the single phase measurement of the dual pole breaker may not account for all the current usage.

Good idea BTW…

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#12

Thanks for your input Spanky,
So, if I had the secondary clamp set, I could clamp all of the phase A devices (three HVAC components) in the same clamp (in the same direction say, from the panel to the device towards the sticker) and then I could pick up something else like the hot water heater.

I am curious about my hot water heating usage as my GE tank is a 2003 and I am considering a hybrid Rheem. When researching the hybrid a suggestion was floated about the useful life of the hybrid vs return on investment. So to have accurate data about my current water heating consumption would better help to make that decision.

After all, “Wood doesn’t grow on trees…”

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#13

Hey @fabricgator - photos of the breakers in question would help with direction here. I recommend creating a new post with those details in it for Community feedback. You’re also welcome to contact support@sense.com to confirm your set-up is correct.

#14

I have an all electric house with 2 panel. Back in Oct,2020 I purchased a Sense monitor and only setup one panel. After I realized we can connect 2 panel to one monitor I punched a second set of CT clamped and added my second panel and did a system reset. Now an error message says it’s reading negative consumption. On the new CT clamps the sun was pointing up and I even flipped them and still get the same message.

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#15

@pipermarc As Justin suggested above, you should create a new thread, or reach out to Sense support directly. This thread is not the best place for your question.

#16

Thanks Brian5 for the suggestion.

#17

Hey @pipermarc - Support team will be back today. We’re currently experiencing some high-volume following the holiday, but someone should will get back to you as soon as possible.

#18

@fabricgator . If I understand you correctly, you’re going to bundle all the wires having to do with heating/cooling into the same CT, and monitor all at once. Did I understand this correctly?

If so, this is a very slick idea and makes perfect sense since one can group the two systems into ‘Climate Control’ … and the only thing left to do is somehow move the breakers closer so that one can bundle all wires together. This approach should really be more wide-spread … assuming doable. That way, we have one extra CT to put elsewhere.

Neat Trick, thank you for sharing!

#19

Hey Justin, I didn’t see your post until now…
I never had a problem or a fault, it is working just as I had planned. All three of my HVAC components run through the same DCM clamp shows everything and anything related to heating my home on a cold evening.

I primarily use the mini split heat pump as a energy efficient marvel and then if the heat pump can’t keep up, the Trane wreck 10kw heat strip air handler kicks in and saves the morning. It all gets documented under my defined title “HVAC Total”

I was simply sharing my novel use and monitoring for our other members.
Sense never really “found” my minisplit heat pump. I got frustrated in that I could identify the usage, but my SEM was merely finding a partial signature yet disregarding the associated 2500w accompanying usage.

Then, even after the later dedicated clamp installation, it baffles me to understand how/why sense identified an additional signature that I am certain is part of the overall minisplit usage (and certainly flowed through my HVAC Total clamp) yet it would ‘pong’ that another ‘motor 2’ had been discovered… (only when using the heat pump equipment)
Perhaps your developers will take my words and improve the product / service.

@drjb
Yes drjb, It works fabulously.
If you read my post above you can kind of get a feel for my setup. My Trane condenser unit and my recently installed mini split heat pump are on the outside panel and the Trane air handler with the 10kw electric heat strip is wired to the adjacent indoor panel.

I simply determined which phase of the indoor breaker (air handler) was phase A, and made two 10 gauge wire loops that flow through the 3" connector conduit, (one from phase A of the mini split, the other from phase A of the hvac condenser unit) while keeping aware of the line / load direction. (breaker side vs component side) and ran them both over to where the air handler breaker was landed. After determining Phase A there, I simply ensured orientation of the DCM clamp and closed around all three wire. I didn’t even get too concerned with getting them all neat and in the center, not sure it maters just so long as the clamp is fully closed and that the installed panel cover wont press open any clamp.
The other DCM is monitoring one leg of my GE hot water heater (the second largest energy hog under my roof)

I was chuggin along heating the front 2/3rds of the house with the 21 SEER MiniSplit heat pump and then just for fun I told "Hey Google to turn on the Nest thermostat heat and set for 73 degrees…
Wow did my consumption skyrocket!

1 Like
#20

@pipermarc
Are you certain that you truly have a second panel and not a sub panel?
If your second panel is fed off of the first panel after the meter, then it is a sub panel.

I suspect that your (all four) clamps are not aligned correctly so your main clamps may be showing xx kw’s and then your secondary DCM’s are subtracting more than it is initially sensing… I hope that makes sense (punny)

At my small 2004 home, 1200 sq ft, My meter and adjacent outside panel are on the outside of the CBS structure. That outer panel lands the 220 vac for the Trane condenser, the irrigation well pump and a few handy GFI 120vac outlets. EDIT: And now my recently added 2 ton, mini split, 21 SEER inverter heat pump… <love it!

There is a 3" pipe that goes out of the back, through the masonry block and into the inside ‘sub panel’ on the other side of the wall. Again, in there, is another “main” breaker (200Amp) that protects that (what I am calling the sub panel) but every electron is flowing from the pole transformer, through the meter, through that outside panel and into my interior panel where all the homes branch circuits are landed.

I put my sense in the inside panel but I snaked my energy monitor clamps through the pipe and I am monitoring the feed phase lines as soon as they come out of the meter can with the primary clamps. That is my total consumption.
I only have a single 200A service although I have two 200 amp panels.

Let us know if that makes sense the way I described it and what you find out. A larger home could certainly have (2) 200amp panels…
It is everyone’s feedback that makes these community forums work. I hate when I read or answer a post and it simply goes dead cold after the poster get their answer. Please let us know if this helps.
Cheers and happy new year