When using two CTs to monitor the two main phases, do I just sum their RMS current?

@moeburn

If you’ve got 100 Amp service, then one question that needs to be answered is how big is the transformer that feeds your house.

Even with 200 Amp service, the max continuously available current is typically 104 Amps.
And that’s only if the transformer (25 kVA in this example) is feeding one house, which
is usually not the case.

See US 200 Amp Service explained or Do I need a 200 Amp CT?
for an explanation of why you don’t actually have 100 Amps of continuously available current, and how to determine the rating of the transformer that feeds your house.

The term 100 Amp service confuses most folks because it means the weakest link in the
Service Entrance Wire, Meter Base, Meter, Main Breaker, Load Center (circuit breaker box) chain, is rated at 100 Amps. It’s not the continuously available current rating.