OpenEnergyMonitor Community

US monitoring two pole circuits without common

Morning folks. I’m just setting up my first IoTaWatt. Works great on single pole, 120V circuits. However, I have a bunch of 2 Pole 240V circuits in my shop that do not use a common leg. I.e., wire is 2 hots & safety ground. Is there any way to 2x the voltage setting on this feed and avoid using two CTs? Really hate to tie up 2nd IoTaWatt channels for single load. Also makes it hard to get REAL power use from device.

Yes, there are several ways.

First, the next release will have a checkbox in the input configuration to “double” the measured value. That should be available as ALPHA auto-update class sometime next week.

Another way is to pass both conductors of the circuit through the single CT. This is a little bit tricky because one of the conductors has to be oriented in the other direction. The advantage of this method is that you can also use it on a 240V load that does use the neutral, like an electric range.

Another method is to use two CTs and combine them into a single input using a stereo headphone splitter. I bring this up because it’s also useful for combining any group of multiple circuits. If you do this, you need to use the same model CT on all of the circuits that you combine, and the combined total current cannot exceed the rating of the CT model.

Last, even if measuring just one leg, you can define an output that doubles the value and you can double it with the scripting calculator when exporting to Emoncms or influxDB.

There is an IoTaWatt specific forum at where you can get information and support for IoTaWatt. Notices of availability of new releases and features are also posted there.

Thanks Bob! This is why I LOVE open source, community supported stuff. Folks that care and know.