Here is a quick exercise:
- Wires for two circuits are entering a junction box through one conduit.
- On the other end, the circuits split into two branches
- Two neutrals entering (current count = 2)
- Two hots entering (current count = 4)
- Two grounds entering (current count = 5)
- Wire gauge is 12, so total volume is
5 * 2.25 = 12.25 cu inches
Does this calculation have to include wires that are exiting? I will have two 12/2 Romex. If this figures into calculation, 2x the volume is needed (24.5 cu inches).
Edit 1: I should clarify that this will be a junction box without any devices on it. On one end, a 1/2 inch LFMC is entering with a plastic connector, and on the other end, two 12/2 Romex wires will exit individually through a snap on connector each.