Ok to splice in two Kasa plugs to each pole of a split AC?

You may be the first if you do it … I can’t see any major drawbacks other than the unfun issue of ensuring that they are always both on (I would disable the smart switch in the Sense interface at least. By NEC code, a mini-split should have a power switch on the compressor (which normally feeds the indoor air handler power) … so use that to switch the unit on and off. If you’re fiddling anyway, do something to prevent activation of the HS110 touch switches.

In theory you could also attempt the Kasa 240V (Euro/Aus) model … as long as you have a mini-split on the smaller side within the current limit.

Just throwing this out there:

The US HS110 plugs are 240v compatible. But there’s no NEC compliant way to wire them up to a 240v load.

If you’re in an area that’s not subject to the NEC, and you’re comfortable doing so, you can monitor a 15A 240v load with a regular HS110.


Good point. If the load is around 80% of 1,800W max … small mini-splits may be fine.
For anything over that the “240V” HS110 has beefier specs. I looked at different country specs a while ago and they vary enough to think that the safe limit is <3.8kW.

Assuming I am not subject to NEC, how could I wire up an HS110 to monitor a 15A 240V load? The AC is fed by two 120v wires 180deg out of phase (as is standard in the US) and has a ground wire. Would I just wire up a three prong plug using the two 120v hot wires where hot and neutral would otherwise be (ground stays the same)?

Yes, that wiring method is correct. Also keep in mind the HS110 rating is based on current, not power, so you can get 2880W through it continuously at 240vac.

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Thanks. I’m well under 2880W. In fact, my Vue tells me I’ve never been over 2000W — maybe because I never heat.

The AC is wired to a 20A double pole breaker. So that protects the wires and AC but wouldn’t protect the HS100 because it would allow 4800W. So if I wanted to protect the HS100 I’d have to downgrade the breaker. If I downgraded it to a 10A double pole breaker, then my max wattage would be 2400W. And as 2400W is under 2880W (when powered at 220vac) then that 10A double pole breaker would protect the HS100. Is that right?



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Good plan.

2000W/240V = 8.3A so 10A will give you a margin.

Regarding, “the HS110 rating is based on current, not power, so you can get 2880W through it continuously at 240vac.”

The HS110 says it supports 15A at 120V. I see online that peeps are saying that it also supports 240V but just doesn’t say so.

So does that mean that it also supports 15A at 240V? If so, it would support 3,600W at 240vac, right?

I’d probably knock 25% off that just because the split AC runs continuously for hours on end. So that would be 2,700W at 240vac which is 11.25A. Does that make sense?

So where does the 2880W come from?


“80%” is the standard derating for wire and whatnot (melting avoidance):

240V x 15A x 0.8 = 2,880W

To get to the finer points, look at the HS110 UK spec for example and notice the variation in max current and power:


With an input voltage anywhere between 100-240V that needs to account for the current phase offset based on the likely 2 of 3-phase supply in some cases. e.g. My house panel is actually 208V between the supply phases because it’s 2 of 3 phases into the building … the phases are offset by 120deg. That results in a voltage of 208V. Lower voltage needs higher current draw for the same power. In my case the peak power potential would be
208V x 15A x 0.8 = 2,496W

For a wye transformer, you can calculate the output voltages … 240V x SQRT(3)/2 = 208V


More generally…

I currently have two 12 gauge wires running through a 20A double pole breaker attached to my split AC. So the AC is running at 240vac. That’s how it was professionally installed and so I assume it’s to code. If code says that a 12 gauge wire can hold only 80% max load if the current is continuous, then that would mean it should only ever have 16A running through it. And yet it’s hooked up to a 20A breaker. So, if the split AC goes bad and somehow starts drawing 18A continuously, then could it not exceed the wire rating yet not trip the breaker. Isn’t that bad? Why would code allow a split AC to be hooked up that way? Or is that not to code? Should they have used at 10 gauge wire?

Now, I’m fairly certain in practice my split AC would never pull anywhere near 16A x 240v = 3840W but isn’t that the point of breakers? To make allowances for appliances gone bad? Especially for appliances that have stepper motors because those motors are designed to slowly step up their draw?

There are legit electricians who parse these threads and I’ll let them weigh in … but having done a good amount of “realworld” electrical work myself, here are some comments:

  • NEC has pretty wide safety margins.

  • Wire length is a factor when running circuits.

  • Wires-per-conduit is also a factor (a circuit is derated if run together with other circuits).

  • Insulation can be an important factor that is open to the vagaries of what constitutes a “professional” install (code rules are debated all the time).

  • Breakers are typically installed to protect the device from overloading the wire (circuit) vs protecting the device … e.g. imagine a crucial medical device that draws 5A on a 15A breaker … it no-doubt has circuit protection built into it … you’d want to provide it with whatever the circuit wiring is capable of providing rather than putting a smaller breaker in the panel because perhaps, in an emergency, the device might get switched out for a higher current one. A “hardwired” device is somewhat different and you can downsize a breaker … but it shouldn’t be considered “device protection” (even though it can be!)

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Admin Disclaimer (@JustinAtSense): This is a potential fire hazard and not an advised solution for 240V device monitoring. Dedicated Circuit Monitoring is a better solution, allowing you to monitor up to 2 120V or 240V devices.

I did it! I used this junction box, to splice a HS110, into a 12/2 wire + this conduit tubing + this male/female plug set for a 240V AC, a 120V pool pump, and a 120V pool booster bump. I replaced all the 20A breakers with 15A breakers.

For the 120V circuits I also used these short plugs.

Works like a charm!


Thanks for sharing.

If you’re going to get another sense for each big item you want to track accurately why not get an energy monitoring system with individual CTs for curcuits?

Because the sense.com app is awesome. The vue app, for instance, is nowhere near as good. Plus, I need the large item consumption to be rolled up into the same reports as everything else — I’m trying to account for all the watts and there’s still a couple hundred always on that I can’t find…

Its 240V circuit. 180 deg difference between the phases.

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I agree that the Sense app and interface is great, and it’s an interesting hobby, but if I can’t accurately measure or be confident in the measurements it makes it less useful. Especially regarding big user items.
For instance I have a HPWH and it’s in an unheated storage room that indirectly heated thru a 14"x8" central air vent I installed behind my fridge in the wall that separates the storage room from my kitchen. That and the 8" duct in the same wall that is currently feeding the HPWH. The HPWH is ‘fighting’ my Mitsubishi mini split as it pulling heat from the house and dumping cold air but I’m assuming it’s still more efficient than putting the HPWH into electric resistive mode. It’d be nice to run it in resistive mode for a week and be able to see how much less electricity my mini split used that week and compare it to how much more the HPWH used. In the summer I pulled heat from the attic.

Sure, but sense is pretty accurate once it detects something or a HS110 has been spliced into the line.

If there’s no plug because the appliance is 240v and sense will not detect then we’re forced to splice a HS110 into the line itself like I did. Is that an option for you?

I bought an amp-meter with a loop so I could see the amperage being drawn and decide whether it was feasible to have an HS110 report the load. You’ll have to decide for urself if ur comfortable with the config…

Good luck!

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Thanks. I don’t mind a few smart plugs or an hs300 here or there but feel that solution is more than we should have to do

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