Do you happen to have a couple 120VAC and 1, 240VAC cube relays lying around? You could hook the coils L1-N, L2-N, & L1-L2, via the 'a' contacts. Use #12 and wire on the load side of breakers for safety. Jumper the 'a' contact of each relay to seal it in and walk away. Indicating relays would add style points. Losing a 120VAC and the 240VAC relay means your losing a leg. Just a 120 relay dropping would clue you in to the nasty floating neutral.
Joe
