Question:

When using a padlock to secure a disconnect device in the "open" (off) state, who should be able to open that lock? In other words, how many other people should share a key to the lock you use to secure a breaker or switch in the safe position, if you are the one working on the system? 

Answer:

You and you alone should be able to open that lock. It needs to be a personal lock, not a lock whose key is shared by other people.