100A CTs or 200A CTs for US 200A service?

I’m very interested in getting an IoTaWatt setup to monitor my house. I’m in the US and my panel and wiring is setup for 200A service. However, I read this article at Open Energy Monitor (US 200 Amp Service explained or Do I need a 200 Amp CT? - Hardware - OpenEnergyMonitor Community) that discusses the fact that you probably don’t really have 200A service even if your panel is setup for it. So, I can’t decide if I should get 100A CTs or 200A CTs from the stuff website with my bundle.

What would happen if, in fact, I do exceed 100A routinely at my service panel and I had 100A CTs? Would I just lose resolution? Or would I damage the CTs and potentially put myself in a dangerous situation with regard to fire in the service panel? Should I just stick with a 200A CT to be safe?



If your MAIN breakers are 200A, I would get the 200A CTs. You really won’t lose much in terms of accuracy, and you’ll have peace of mind that the CT’s are properly sized for the maximum load your panel can handle.

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Thanks for the feedback. Yes, I have 200 A main breakers. I was concerned that going with 200A CTs if I never really went over 100A would reduce my resolution too much, but, I would always be concerned about exceeding the 100A limit at some point if I went with 100A CTs. I think you’re right that just going with 200A CTs is the best choice here.

Now to search if people prefer the AccuCTs vs bigger ECS25200 clamp-on ones. I guess, if you have the space behind the panel cover, the clamp-ons would be easier to manipulate.


Not an issue at all.

It’s kinda the other way around. The clamp-ons make it easier when you don’t have a lot of room. I f your cables are in the clear, the split core are cheaper and are 0.5% vs 1% for the clamps.

regarding the 100A. It’s true that most 200A never exceed 100A, but other considerations are future growth (everything is moving to from fuel to electricity) and the size of your cables (100A are only 16mm).


I hadn’t pulled off my panel cover yet, so I did to take a look. Looks like I’ll have plenty of room for either choice. The hardest part will be dealing with the cabinet they built around it when my basement was finished. Wish I’d done this years ago before it got closed in. Will probably punch a knockout out of the bottom and come through there since that’s about the only open space around the enclosure.