I’m looking to monitor my house’s entire electricity consumption using CTs (current transformers) installed in my breaker box. I have 200A split phase service, the most common kind of residential electrical service in the United States.
I tried using the Shelly EM system recommended by the Integrating your electricity grid page in the Home Assistant docs, however the biggest current transformers Shelly sells are physically and electrically too small for 200A service. It should be noted that all Shelly systems are incapable of monitoring 200A service. Their products are designed and marketed primarily in Europe, where because the residential service voltage is higher, the amps are smaller, and thus the cables coming from the utility are smaller, and thus they actually fit in the tiny CTs they sell. (Because they can’t be used to monitor whole house power in most homes in the United States, it may be worth updating the web site to point this out, to prevent people from accidentally buying it in the future, like me. Fortunately I’m still in the return window.)
So if not the Shelly, what else is out there that is Home Assistant compatible and doesn’t require bouncing data through the cloud first? To monitor standard US residential service - split phase 200A. I need 3 CTs, physically large enough to fit over 3/0 awg cables (L1, L2, N). Uses wifi or I can run an ethernet cable. Ideally it is a complete product and not something I have to piece together like an ESPHome based system, but if that is really the only way then I’ll do it.
@tom_l Thank you very much for the link, this product looks great! I notice it only measures the voltage of L1 for reference, not both L1 and L2 like other meters do. Do you think this will impact the accuracy?
You can add extra voltage transformers so it has a separate reference for each phase, but you shouldn’t really need it. The voltage should be pretty close between phases.
@sparkydave How do additional reference transformers attach to the device? I thought I saw only one port for it.
I have solar power here, with two 10 kW inverters in parallel with the mains on my house. When I overproduce, power goes the other direction. Would that impact the voltage difference between legs?
Thank you for explaining. They are split phase just like the utility, two 120v legs come out of each inverter, the legs from each inverter are combined in a sub panel, and two legs come out of that to my ATS, and 2 legs come out of that to my breaker box. Sorry it’s a bit complex here. I appreciate the help!
No problem. So you have the option to either run two VT’s or using the ‘inferred voltage’ for the second phase and assuming that the voltage will be pretty much exactly the same across the two.
I’d love to run two reference transformers but I don’t have room for a second power outlet for that leg by the breakers. Is there any way to use a wire connected to a breaker like some power meters do?
Sort of, the iotawatt only accepts a 9Vac nominal voltage reference but you can use your own transformers. There are examples of people doing this on the iotawatt forum.
I have my iotawatt in the roof space above my switch board and just have the CT cables running down into the board to pick up each circuit. I installed an outlet up in the roof space next to the iotawatt for the VT and USB supply. I could have installed two more outlets and run two more VT’s (I have 3 phase power) but I couldn’t be bothered.
I just read a few posts on the iotawatt forum about different Vt configurations, but I realized that I’m truly only interested in obtaining the sensed current in amps. I have a very accurate 240v voltage reference by way of my solar inverters (which are integrated into home assistant). The iotawatt UI is really nice, but I’m mostly interested in home assistant, so in home assistant I could add up the current readings from iotawatt, and multiply by the voltage reference from the inverter. I think this would be just as accurate as measuring each 120v leg separately? What do you think?
Thanks again for your help on this forum and the iotawatt forum!
For the sake of a cheap VT I’d probably just install one of them anyway so you get the iotawatt to do some internal calculations for you (such as calculating power and providing it directly rather than having to do it in HA).
