why ganged breakers?

Doesn't sound like these are heating circuits, but General purpose ones.

Either there's a shared neutral, or the wiring from both circuits goes into a common junction box (which doesn't require ganging, but some people do for safety), or someone was stupid -- after all they missized the breaker so they could have mis-applied it as well.

-Tim

How do I check for this type circuit?

There is a chance that those two circuits are sharing a neutral (an Edison circuit). It is a good idea to keep them ganged so that no one will accidentally but them on the same "phase" in the future.

Steve B.

Do you have electric heaters on those circuit? I would suspect that someone ganged the breakers with two wires instead of using one heavy wire.

If the two circuits are both going to the same outlet, then the breaker should be ganged. (From what I have read) If not then someone probably just used what was available. But I wouldn't ungang them unless you can map out the circuit 100%.

"Normally" there will be a red wire to one breaker and a black wire to the other. And "normally" they will trace to a common cable with a single white.

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.