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

To detect my pool pump I re-wired it to use use 120V and spliced in a Kasa plug – first I spliced in male and female 3 pronged plugs and then stuck the Kasa plug in between 'em. That worked fine and now I can see my pool pump.

Can I do something similar with my split AC?

The split AC runs at 220 on a dual pole 15A breaker. Can I splice in two Kasa plugs, one for each 15A pole, and monitor the split AC that way? I could merge the two Kasa plugs into a single sense device. Will the injection of the Kasa plugs throw off the phases of the two poles so that the AC wont work? Or should it work just fine?

Thanks,
Chris

In theory you’ll get some data … the inline Kasa won’t do anything to the current phase.
I assume it’s 240V and not 208V.

In practice, get another Sense and dedicate it to the mini-split and another 240V device on the solar CTs … or if you don’t have solar, get the solar CTs for your existing Sense and you can put them on the mini-split.

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Hm, In theory, wouldn’t the data be perfect after merging the plugs? By perfect, I mean it would just capture the AC like any other device and roll up its usage in the reports. And yep, it’s 240V total fed by two 120V lines.

The reason I’d rather not get another sense is because the data would not be integrated with the rest of the house and so the dashboard overview of my usage would be incomplete.

I can’t be the only one for whom split AC represents the majority of their usage and so would endeavor to disaggregate that somehow. Has anyone tried two Kasa plugs? Or is everyone just waiting for sense AI to figure it out?

Thanks,

Chris

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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.

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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?

Thanks,

Chris

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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?

https://www.icmag.com/modules/Tutorials/ElectricalSafety/1655.htm

“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:

https://www.tp-link.com/uk/home-networking/smart-plug/hs110/#specifications

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

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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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