A few years ago a contractor added two 20 amp lines from the breaker box to a knee wall on the second floor where they terminated in a junction box. They were put there for future use in a central AC system.
We did add central air eventually but those 20 amp lines weren't used (so I thought). I was going to connect to one of those lines the other day so I could add an outlet to a wall without any, and noticed that inside the junction box those 2 lines were connected and powering a 12 awg wire which I haven't traced yet.
Is it safe to have those 2 separate 20 amp lines, each on separate single pole breakers, connected to each other? Does that connection create 240v but still at 20 amps?
Here's a photo of the junction box: