2002 NEC 408.20 (the paragraph after the Exception)Grounding (ground) conductors shall not be connected to a terminal bar provided for grounded (neutral) conductors unless the bar is identified for the purpose and is located where interconnection between equipment grounding conductors and grounded circuit conductors is permitted or required by Article 250.

2002 NEC 408.21 Grounded Conductor Terminations.- - Each grounded conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor.- - - Exception: Grounded conductors of circuits with parallel conductors shall be permitted to terminate in a single terminal if the terminal is identified for connection of more than one conductor.