A typical utility spec, from
http://www.pge.com/customer_services/business/tariffs/doc/ER2.doc for 240/120V service, lists minimum 3-phase connected load of 5 HP—up to 500 kVA maximum demand.
Realistically, from copper-savings and starter-size economy, it would be common for a maximum connected/combination 230V load to be roughly 25-50HP. IMO, an approximate 240-versus-480V breakpoint seems to be about 30HP for single motors. Where 480V is served to a facility, it’s routine for 1HP and up motors to be powered at this voltage. Motor catalogs list stock dual-voltage [230/460V] 3ø motors starting at
1/8 HP.
From a safety aspect, note that 240/120V∆ has one phase 208V-to-ground. 240V corner-grounded delta is 240V-to-ground on two phases. 480Y/277V has, of course, 277V-to-ground on three phases. The relative difference in potential shock hazard for these typical service voltages is not markedly different.
