I believe that's how it is throughout most of the US, WFO, but there are always areas with wierd setups.
kmt, mostly, US distribution is high voltage 3-wire 3-phase delta, with ground wires strung above more as lightning rods than anything else, and grounded at every tower- the earth itself carries the lion's share of the unbalanced return current. This is stepped down to medium voltage in regional substations, sometimes in multiple steps.
Power run on the poles into residential neighborhoods is typically medium voltage 3-wire 3-phase delta (again with a small ground wire atop, grounded at every pole, or every other pole). Then, a small transformer will tap 2 of the phases. (Or, in my neighborhood, there is only 1 MV wire run with no ground, and it's tapped straight to the earth.) The secondary is a center-tapped coil with the center tap grounded to the earth so that either end is +/- 120V to ground and 240V between them. These 2 wires are run along the street, where several houses will tap off it to their respective service panels, where the ground is again grounded to earth, and neutral bonded to that. Most individual circuits are 15A or 20A 2 wire (120V/neutra) plus ground. Larger loads use 3-wire + ground 240V.
Commercial and industrial sites will often get 3-phase power (stepped down from MV to LV at a transformer right outside the building), sometimes delta, sometimes wye, and at a variety of voltages. The most common I've seen are 208/120V and 480/277V, but there are oddballs, too. The neutral is always derived at the switchboard and in every wye-secondary transformer.
[This message has been edited by SteveFehr (edited 08-14-2006).]
