Pre-purchase Research Question

Hello all. I was just reading this post - 400A service, 3 panels, and lots of unused circuits - since right now I’m trying to determine the best way to combine 3 circuits into one IoTaWatt input without overloading the input. I have 3 double-pole 240V breakers. First is a 20 Amp with a neutral, second is 20 Amp GFCI and third is 30 Amp no neutral. What I am putting out as a potential set up is to monitor both legs of all three circuits using two 100 Amp CT’s. Running all 3 Phase 1 lines through CT #1 and all 3 Phase 2 lines through CT #2 then combining the with a splitter. The sum of the max Amps would be 70 Amps. Would the sum of the CT’s output be too much for one IoTaWatt input? Realistically, current will never come close to the max since one 20A circuit is for a table saw, another for pool pumps and the 30A is for three strips of electric baseboard heat. Better ideas welcome in addition to my question. Thanks.

That works. There are two rules when combining CTs with a splitter:

  1. All of the CTs that are combined must be the same model.

  2. The sum of the amperage of the combined circuits should not exceed the rating of that CT model.

So what you describe should be fine. The three circuits total 70 Amps and the CT model can handle 100A.

Now you bring up that these circuits may not actually operate at that amperage. Circuit breakers should be sized so they are loaded to no more than 80% of their rating. So the expected maximum load in your case would be 56 Amps. The 50mA limit for an IoTaWatt input is a little understated. In reality, they can handle about 57mA. Moreover, no harm will come from slight overloading. So long story short, you should be able to use 50A CTs.

Excellent info. Thanks a lot. I believe I will go with 50A CT’s. Soon time to wrap up learning and planning and place an order!