Newbie Questions - for 240VAC

I am looking at getting an IoTaWatt to monitor my 240VAC US split phase system, and have some confusion about how/if it can handle some of the circuits in my house.

In particular, I have some confusion about how it handles 240v loads. The manual spoke of using a single CT on one hot lead and configuring it as double. Fine for pure 240v loads (water heater, etc), but not ideal for appliances which may also pull 120v from the connection. Can IoTaWatt measure such mixed voltage loads as a single use point?

I also have questions regarding circuits which are bidirectional (eg an inverter which will both pull power from the grid as well as send power back at times). I have a grid-tied (net metering) 120v inverter which will send power back on one 120v leg, the same leg that it also will draw grid power from for its loads. I would like to meter its power usage and generation at the breaker which connects this inverter, as well as monitoring power usage at the top of the panel (to see how much of this inverter power is being used vs sent back to the grid). Is this possible with IoTaWatt? I also have the same question for a 240v inverter.


Without getting too deep in the details, IoTaWatt can do all those things.

Regarding the 240 Volt loads, the docs distinguish between two-wire and three-wire loads. If the load does not (or use) a neutral, the “double” works well. For three-wire loads, there are a couple of approaches:

  • You can use two CTs, one on each hot lead, and create an output that adds them together.

  • You can pass both hot leads through one CT in opposite directions.

See the docs for details.

Where you have bi-directional power flow, checking the “allow negative values” box will cause the power to read positive in one direction and negative in the other. The datalog will show the net. If you want to know the total positive and total negative, you create an integrator to record those values.

See the docs for details.

Thanks overeasy. I will check the docs for those things.

One other question I have is how much data can be stored on the unit and for how long. I am thinking of using this in a place which has no WiFi, and was wondering if I could run it without any WiFi connection for a while (few days?) and then bring the IoTaWatt unit back to a location with WiFi access and access the data. I guess it would need sufficient storage for however much data, and the data would need to be persistent over being powered down.

Ten years. Better to leave it running and use a phone hotspot to connect to internet if service is available.