ANSWER: The presiding officer should make every effort to maintain an appearance of impartiality so that members on both sides of any issue can feel confident that they will receive fair treatment. To this end, the chair does not participate in debate or bring forward a motion on any issue unless she has passed the gavel to another officer.
The presiding officer may participate in the voting in the following circumstances:
1) the vote is by ballot
2) the chair's vote will change the result of the vote (i.e. the vote can break a tie for a motion to either pass or fail or the vote can create a tie).