Options for 240V split-phase reference and power

Looking to dump my emporia so I can integrate with HA but don’t think I am a good candidate for iotawatt. I have an exterior panel with 6 240v breakers directly feeding a sub panel and 5 large draw appliances. This means I have no 120v beakers in this box and unfortunately no exterior plug near by. I also don’t have any open breaker slots. What options if any (short of running a new drop from the subpanel) do I have for powering and reference? Can it run 240v with a different accessory or something?

The emporia is only monitoring my subpanel (due to connecting to 120v breaker) and other than the fact that I don’t like it, is the reason I am looking to move away.

Don’t want to buy a Sense but it might be my only option because I can directly connect it my one of my 240 breakers and it works with HA.


You can run a Euro 230V transformer. The only issue is that it has a two pin Euro plug. I use one in my home using a Euro power strip. I changed the plug to a 240V US plug (one blade is sideways) and installed a 240V socket. You could just as easily hardwire it.

Both the US and Euro USB supplies are switching power supplies that work from 90V to 270V, so you can also use the Euro USB supply with two-pin plug.

When using a 240V transformer in the US, you cut the calibration factor in half to read 120V and it’s all good.

I have the EXACT same setup as you, and I was able to find a very elegant solution as shown in the following post. I had to replace one of my 240VAC breakers with a special “tandem” breaker that gave me two 120VAC breakers in addition to a 240VAC breaker. It has worked great!

Thanks for the reply’s. Its nice to know I can get to work the way I want it and not be forced to use an inferior product. Based on this feedback I am going to purchase and pull out my other monitoring solution. THANK YOU!!

@warblingly Technically the tandem breakers might be a code violation for you if you don’t have a main circuit breaker— your panel sounds like it uses the “6-disconnect” rule instead of a main, so adding a breaker would not comply with code.

I find myself in the same situation and will need to convert my existing main panel to a main breaker only, and then add a new distribution panel nearby to re-feed everything from. (Also makes it easy to add more solar, batteries, and a backup generator.)

You raise a very good point, and I very much appreciate you bringing this to the community’s attention.

I have been doing a little research to better understand, and I am wondering whether or not the exception listed in the following NEC sections for “Power Monitoring” might apply in the case of the IoTaWatt?

Unless I’m missing something, it’s not clear that this panel does not have a mains disconnect. Maybe a picture would help. At the end of the day, the user is responsible for complying with regulatory requirements, so if there is a question of compliance and/or grandfathering and/or exemption for monitoring, that should be directed to the local compliance authority or a licensed electrician.

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@ogiewon It wouldn’t comply if it is a standard receptacle that the power supply and voltage reference are plugged into as I understand it, unless it is installed in a way that it could not be used for general purpose.

@overeasy agree that this forum isn’t the place to get into electrical code requirements, just wanted to point out the risk.

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Hmmm… :thinking: How about having the electrical receptacle inside a locked box?

@ogiewon if you put it in a box with the Iotawatt then you should be fine. Don’t even need a padlock, just something to define its purpose.

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Yes. You are correct in that I seem to fall under that and don’t have a main disconnect, just the six breakers. While I assume I am grandfathered due to being compliant at the time of construction I believe I am unable to make changes and still be considered compliant under the old rules. Maybe the euro plug is the way to go. I will do some more research. Thanks all for the input.

My box is just like example A in the picture that ogiewon posted.