In article , Rick-Meister wrote:
This could also be two circuits that use a common neutral. That would
happen if you ran 12/3 like in a kitchen where the top receptacle is
on one circuit and the bottom on the other, but they both share the
neutral. Code requires that the breakers be tied together so both must
be shut down to avoid killing somebody who thinks they're working on a
dead receptacle.

Actually, Code doesn't require handle ties, unless there's a 240V device
somewhere on the circuit. IMHO, it *should*, but it doesn't.