Two meters, four panels, how many IoTaWatts?

I’m trying to design a system to accommodate my house’s power system in the US. That system consists of:

  • One 200A split phase main panel with 100A branch panel
  • One 150A split phase geothermal panel with 80A branch panel

Each primary panel is fed by a separate meter. The primary panels are in the house and the branch panels are in an attached guest/office space. I have substantial loads on each of the four panels that I’d like to monitor:

  • A geothermal heat pump and hot water heater on each geothermal panel
  • Household appliances on the main primary panel
  • Pool and server rack on the main branch panel

Does each meter need an individual VT and thus one IoTaWatt per panel, or can I have one IoTaWatt for each location?

Each IoTaWatt requires a voltage reference, however they can share a VT using a standard CCTV splitter. The only limitation is distance between units and thus availability/practicality of extensions. I would recommend against sharing a VT between units that are monitoring panels on different meters.

You can monitor a branch panel in it’s entirety using CTs on the feeder circuit in the main panel.
To measure individual circuits in the branch panel, you would need to use another IoTaWatt or extend the cords on the CTs back to the main panel. You can extend CT leads using standard headphone extensions up to about 25’. Some have reported success at greater distances using CAT6 to extend 4 per line, one twisted pair per cord. Adding 3.5mm jacks and plugs makes it pretty clean.

I do want to mention that aggregating the data from multiple IoTaWatt will require using a database like influxDB. Given that you have a server rack, that sounds like something that you can handle.

Thanks! To restate:

  • Each meter should have it’s own VT, which means a minimum of two IoTaWatt kits.
  • I can monitor branch panels as a whole from their feeder circuit
  • If I want more granularity (i.e. I want to monitor the pool separate from the server rack) then I’ll need another IoTaWatt on the branch panel. Extending CTs is not practical, there’s no easy route and the panels are at least 50ft apart.

Aggregating in influxDB isn’t a problem. I’ve been planning to set it up for Home Assistant anyway.


If you want to monitor a lot of circuits, IotaWatt is great. I currently have two and am considering getting a third. If you want to monitor individual loads, I like using power measuring devices running Tasmota. I already use (mostly) Sonoff devices running Tasmota. I am upgrading most of them to ones that also support energy monitoring. This is mostly to get more positive feedback that the thing I turned on is really on. It also has the benefit of providing more data that I can integrate on my Grafana dashboards.

Depending on what you want to achieve with the data, you might need to use the latest InfluxDB in the 1.8 series that supports (but doesn’t require) Flux queries (which support math across series). IotaWatt does not support InfluxDB 2.0, since it requires Flux queries, which IotaWatt doesn’t support, currently, at least. I have not found anything that requires InfuxDB 2.0, so this constraint is fine.

You will need the latest Grafana to use Flux queries. InfluxQL support in Grafana is better/easier to use and works for most things. You can stack graphs in Grafana, which will give a visual indication of combined load, or you can use Flux to do the math with a single line. The Stat panel can reduce a plethora of query results to as little as a single number, but some of the reductions don’t really make sense.