Why measure the mains?

Why am I measuring the mains into my house? Why not just measure all the branch circuits? All else can be derived. (My case is a USA based 120/240 single phase, 3 wire system.) It’s not a huge difference, but it could free up two more CTs to refine my measurement elsewhere.

I can see how one starts this way. One might start with only a few inputs, so it’s obvious that one has to include the mains. And with some other systems, there might only be 4 or six inputs available. My pre-iotawatt system had only 4-ish inputs, so I did the mains, my solar and my car charger. And so when I bought the iotawatt, I set it up the same way, even though I started out with a full load of CTs. That is, I set it up basically as the previous system, but with more refinement. Of course, 14 CTs is not quite enough to do every single breaker in my house, but if I double up on few, I can measure every single circuit.

I have created a “checksum” output of all the loads added together vs the two mains, and the difference is usually about 6 watts or less. So the derived amounts are pretty accurate.

You can do that. I guess most folks have a lot of very low use/uninteresting circuits and find it easier to do fewer circuits and compute the “unmeasured”. Six Watts variation is pretty good.

I have too many (at least) moderately interesting circuits to fit in two Iotawatts, let alone one. I like having the mains as an easy to process number. But, you are correct if you have a small enough panel it isn’t necessary to measure the mains.