Lyle,
The PoCo doesn't supply a separate earth connection as in TN-S.
All services in the U.S. are arranged as what would be called TN-C-S or PME over here. The building's earth system is always bonded securely to the supply neutral, along with bonds to ground rods (or rings), water, gas, etc. In fact, at the main distribution panel the neutral busbar is bonded directly to the metal casing (isolated at sub-panels).
The NEC actually prohibits the use of TT systems which are common in Britain & Europe:
250.4 General Requirements for Grounding and Bonding.
(A) Grounded Systems
(5) Effective Ground-Fault Current Path. ..... The earth shall not be used as the sole equipment grounding conductor or effective ground-fault current path.
[This message has been edited by pauluk (edited 03-08-2003).]