Bob,
I'm just saying that handle ties would let you use one lock in place of 2 or 3. These locks are required any time you are working on a grounded conductor of a multiwire branch circuit. If you are called in on a service call to work on a receptacle, how would you know if it is part of a multiwire branch circuit without doing a physical trace of the circuit? There is no code requirement that multiwire branch circuits and their grounded conductors be identifed as such. There isn't even a requiment that the breakers be installed next to each other. You can use circuits 1, 9, and 17 as a multiwire branch circuit just like you use circuits 1, 3, and 5.
Don
