Not to make things more difficult, but if you have 3 phase available at your service, the SERVICE PANEL should be be 3 phase. That’s because it’s important to have balanced loads on the 3 phases IF you have some 3 phase loads, especially things with 3 phase motors. If you feed single phase sub panels from there with 2 pole breakers, that’s allowed, but it becomes more difficult to make sure the loads are balanced. For that reason, I always recommend using 3 phase sub panels and just feeding single phase (and/or 3 phase) loads from them, paying attention to balancing those loads.
But sometimes when you have a system, such as an apartment or condo complex, where all of the loads are single phase, load balancing is not as important and all of the sub panels can be single phase. One reason is that most residents will not be able to understand 3 phase distribution and although not really a technical problem, it can be a nuisance for managers to keep answering questions (been there, done that). Unbalanced loads might affect the transformer and utility primary, which is why we should always try to balance them as best we can, but really that’s more their problem.
