How do I check for this type circuit?



Trace the two wires back up the panel to where they enter and see if
you are dealing with on cable (two hots, one neutral and probably a
ground all in the same jacket) or two separate cables.

If you only have one neutral then it is an Edison and should be on a
ganged breaker but there is no requirement to do so. The reason it is
a good idea is that current on one leg balances out the current on the
other leg so if you have 15 amps running on one leg and 10 on the
other the neutral is carrying the difference of 5. If you
accidentally got both breakers on the same leg then the balancing is
gone and now you have 25 amps running back over the neutral which is
more than it would have been rated for.

Steve B.