Problem:

Trying to add 84 branch breakers into my panel, but no matter what panel type I choose it still shows errors.

Solution:

If you are unable to add the breakers you want, it may be due to having a main breaker that takes up too much space to allow for 84 circuits.

If the main breaker is 400 Amps, then in a P2 you can add a maximum 66 poles. (this is not including shunt trips, surge or anything other than breakers.)

The P3 still has 80 inches of unit space, so with a 400A main you still can only have 66 poles. The P4/P5 have 90 inches of space, which allows for 12 more poles or 78 poles total, but a much more expensive choice than a 2 section panel.

Summary:  Use 2 sections when building a 400A Main Breaker Panel requiring 84 circuits.