[The Deez]

here it is straight from the nec

210.4(C)
Line-to-Neutral Loads. Multiwire branch circuits
shall supply only line-to-neutral loads.

Exception No. 1: A multiwire branch circuit that supplies
only one utilization equipment.

Exception No. 2: Where all ungrounded conductors of the
multiwire branch circuit are opened simultaneously by the
branch-circuit overcurrent device.

 

[The Deez]

This section to me has been a topic of confusion more than once, but im leaning in the direction that you MAY do this as long as they are the same amperage, and have a simultaneous disconnecting device, thinking logically, if EITHER of the two legs exceed amperage, it will trip both legs, and on the other end if you need to shut of either of the circuits for service, you will be forced to shut off both to eliminate the hazards of neutrals....

Agreed, I've only been a licensed electrician for about 10 years. All i have to go by is past experience, and i can honestly say that I haven't done this, nor would i do it and I can think of LOTS of times I had the opportunity to do this wiring method. If it was me and in my opinion i would just run a 12/2 for the 120v stuff and leave the 240v stuff on a dedicated circuit. This is an interesting topic though, I have a meeting with a state inspector tomorrow in Boston for a job, I'm gonna run this by him and see what his opinion is. Maybe he can reveal a secret code article.