He is saying for open delta services you should have two seperate load calcs, one for single phase loads, and one for three phase loads. So basically you do the load calcs and add the demand ampacity together at the end. Is this correct.

Typically with open deltas I have a minimum of two panels, one three phase which I feed all my three phase loads from, and then I feed a single phase panel from the three phase panel using the A&C legs, and I feed all my 120V single phase loads from there. I know I could technically just use the A&C spaces in the three phase panel but I always run out of spaces. Anyway when im done, I only have one load calc and I calculate the required service size using a voltage of 240-3.

If I did it like the designer suggests, I would have two load calcs one three phase and one single phase, one would have a voltage of 240-3 and one would have a voltage of 240-1, the result would be the sum of the amps.

Thanks guys.