Mini Split Dedicated Circuit - wrong setup?

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.


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!

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.
image
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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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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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…

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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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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.

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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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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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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