The protected players list is another one of those things for managers to protect against themselves in the league.
To my knowledge and this is in no way confirmed by any official source but I do believe that each manager can have 5-10 players on their protected list each season this is usually used by teams that are always uncertain about their own players who are NHL drafted prospects and are eligible to return to the league the following season.
Typically you hear about 1-2 players who are on protected lists each season however its very rare for teams managers to know who they may have come back from the NHL.
It would be interesting to see what the actual number of projected players is for each team but in no way easy to confirm.