Here is a previous thread on this very subject. http://discussion.autodesk.com/thread.jspa?threadID=507447
The idea is to select an already placed panelboard. Open the particlar family in question by hitting the edit family button. Do a save as so that the original type is preserved. Once the editor is open, select the electrical connector and push the properties button. The connector looks like an X,Y,Z ucs icon. In this dilaog box you can select how many poles you want a device to be under the parameter "Electrical - Loads".
Hopefully this helps. If not, then go to the link I inserted. Have a good day.
Rob McCarty
Ideate, Inc