Physical Setup Advice / CT Distance?



First I’d like to say the IoTaWatt is freaking awesome!!! I’ve been waiting for an opensource solution for a decade. Thank you for creating something that doesn’t report all my usage to a cloud provider and leave me with a cheezy mobile app.

I definitely want to install a system, but my house is a strange configuration and I’m wondering the best way to set everything up.

My meter is on a pole outside (~15ft. from the house). The “main” panel (outside) contains a well pump and generator (input). I plan to also add a sub-panel in the outside panel for a detached garage (which I’d also like to monitor).

The outdoor panel then feeds the house where there is another “main” panel with the (22) inside circuits.

If I add an IoTaWatt inside the house, I won’t be able to monitor the “true mains”, well pump, generator, or future garage current.

If I mount it outside, I won’t be able to monitor the (22) circuits inside the house.

Does anyone have ideas how I can monitor circuits from both panels (hopefully with minimal hardware)?

Can CT sensors be ~30 feet from the IoTaWatt through conduit with high voltage cables? i.e. Mount an IoTaWatt inside & run 5 CT’s outside for the “true mains”, well pump, generator, & garage circuits.

Or do I need a unit outside (EmonTX?) and a separate unit inside (IoTaWatt)?

Side question… If I have 22 circuits and 14 CTs, can I double up seldom used circuits (basement, attic, etc.) by running both wires through the same CT?



I think you’ve got a few options:

First, with respect to the outdoor panel, the only load I see right now is what I assume is the well pump connected to the only breaker (besides the main). Not sure where the generator is wired in.

If the well-pump is the only load out there, I’d suggest you just not measure it for now. Typical domestic use is not high, and it is also fairly constant over a month. Moreover, it’s usually not a load that you can save a lot on.

CTs can run 30’, but running them in the main conduit is a code question that I think would be a no.

The EmonTX is not compatible with the IoTaWatt. It transmits to one the OEM base units using radio. To monitor real power you would need an AC reference transformer in addition to a USB power supply out there.

There are a variety of methods to monitor multiple circuits with one IoTaWatt input. You can do as you describe, passing a conductor from each circuit through a single CT. You can also combine multiple CTs with a standard headphone splitter if you observe some simple rules. Or you can do both - combine several CTs, each with one or more conductors.

What might work out is putting the IoTaWatt on the main indoor panel and ignoring the well pump for now. When you add the garage sub-panel, you can consider adding a dedicated conduit back to the house for CTs. I usually recommend using CATx wire to handle up to four CTs.


Thanks for the quick reply. It must be true that you don’t sleep ; )

I suppose monitoring the outside panel can be a future project. It’s winter here anyway. Good point about needing a reference transformer and additional power outside for Emon equipment (thanks).

The open panel pics are old. Currently there is a generator in the top right with an interlock kit. Well pump moved to top left, leaving space below for a (future) 50A sub-panel.


I would like to see the well pump cycle to monitor/log when it’s running, total hours running, etc.

I suppose a CT for the generator isn’t necessary if I monitor the mains from inside the house.

Then I would only need to run 2 CTs outside. One for the pump, another for the (future) garage.

“Inside Mains” + Well Pump + Garage = Grand Total

I’ll start on the inside panel and expand from there.

Thanks again.


I see no reason you couldn’t acquire some 600v shielded twisted pair wire which should accurately be able to shield the communication of the CT over a distance within a shared conduit. As for the 30’ distance and whether that is too long I can’t accurately say.