Cable Sizing

Your cable size should follow the appropriate building codes. This will follow the maximum current your service can provide, not the current you draw.

Cable rating is for maximum of the designed load, plus a percentage derived from the tables of your local design authority. You don't have different cable sizes for each phase, that's for sure.

Since you have the usage for each, I would continue with that and complete a full power quality survey for each panel and subpanel to figure out why you are imbalanced between phases. You have to take into account the sizing of the neutral and the rating of your transformers to make sure you design a healthy system. Since I see a 75% difference between your 2-3 you will want to check into that. You must also determine your reactance and PF for the system. There is so much to go into it is too much for this forum.

As far as the formulas go, you can google them or use your handbooks from your local authority.

There is a table the gives cable ampacity located here. However, there are

code rules that may require you to use a different size. You need to get someone who is capable to assist you in this selection. Maybe an engineer.

Hi.

your table is usefull . thanks

Having trouble with British Standard 7671, eh?