William-

Noozer did his best to answer your question.

Personally I was not able to understand it clearly enough to answer
it.

So unless you are willing to restate your original question more
clearly I sincerely doubt you will get a better answer.


:"I would like to confirm that, according to the NEC, there is no
reason
why you cannot use 12/3 connected to 15 and 20 amp breakers (one on
pole A the other on pole B) and then (say 30 feet away) branch into two
circuits (a 15 amp circuit on 14/2 and a 20 amp circuit on 12/2).

So does this mean you'

running 12/3 from a 15 amp breaker
& also running 12/3 from a different 20 amp breaker

or have you created a shared neutral situation?

???

and then ~30ft away "branch" (branch what or which; each original
circuit ?)

into two two circuits (a 15 amp circuit on 14/2 and a 20 amp circuit on
12/2)


is each original circuit be branched or just one of them?
do you intend to install the proper sized breakers to protect the 14/2?

bottom is 12/2 ok on 20 amp breaker, 14/2 is only ok when protected by
a 15 amp breaker

fyi when you're asking for free advice try not to **** of the guys with
the answers.

why the mixed breaker & wire size?

Just run it all in 12/3 & simplify your life.

cheers
Bob