Hey Ward,
Thanks for the question. You are exactly right with this drawing and installation. The CT ratio you use for your multiplier is 400:5 / 2 or 40:1.
This connection, even though it uses 2 CTs is seen as a two turn CT wiring connection.
Many metering folks have this question often, so it's fun that you used and referenced my book to ask your question. That was great.
Happy to answer any other questions you may have.
Take care and Be Safe All Ways,
Brad
I installed a form 3s single phase 3 wire from book 1 drawing 14, my question is on the multiplier, I used two 400:5 ct's do you half that?