Can I convert one existing 240V circuit to two 120V circuits, using the one existing neutral for both new 120 circuits? How?
Yes it is called a multiwire branch circuit. However proper care of terminations is required.
Yes, you can. But I would never recommend it. It can be very dangerous and a real headache to troubleshoot. Everything Must be labeled at all terminations. If you ever had to remove one of the circuits, both circuits would fail. This is one thing I wish the NEC would make illegal.
Handy Andy In Mt Airy NC
You must have a four wire feed to do this. You cant do this with a three wire feed.