You have to work out which is what - delta's always the lower voltage, star the higher, and there's the root 3 factor between them - it's easiest to picture it through a bit of basic geometry: a delta has the line voltage on the sides of the triangle, e.g. 240v between phases, if you then rearrange the three sides (the windings) in a 3-pointed star with 240 on each, measuring across the points will be 415v and at the centre where they join, the "star point", will stay at zero - this will (or can, it's not needed) be the Neutral.
Only time this goes out the window is with medium-voltage motors, usually in the 100HP class, where the 3-phase voltage can be anything from 660 - 720v to 3.3 KV - I don't play with those, they're scary!
This is how most of the world distributes power, 220 - 240v (now "harmonised" to 230v +/- 10% in Europe) phase to neutral, 380 - 415v (400v harmonised)phase to phase. The phase to neutral service is in most homes, where it's normally only one phase and limited to 80 - 100 A, 3-phase for commercial and industrial up to about 400A, then for even more you get your own substation transformer down from 3.3 KV or 11 KV to 415/720v, that'll supply quite a bit of power...
Dave H. (the other one)