Sizing Main Circuit Breaker for Three Phase Electrical Panel

[Benihana]

How should I size a main circuit breaker for a three phase electrical panel? Should it be based off the connected load? Off the highest phase's amperage? I've been taught at my company to base it off of the connected load when designing.

 

[ptonsparky]

I did it from the calculated load. Seldom, if ever, an absolute minimum.

 

[infinity]

As Tom stated the load calculation would be the minimum, good design might leave some additional room for future loads.

 

[Elect117]

You can always use the panelboards rating as well. If you are talking about sizing both the panel and the breaker then there are methods in the NEC to use demand factors on loads to reduce the sizing.

For the most part, 220.87 works the best for existing places. For new, then I would over size to allow growth.

Nothing is worse than having a brand new spanking building with a huge floor area and the service is sized for just the general lighting. Any tenet or future owner will have to swap that out to bring in some forklift chargers or machinery.