According to J T :
Interesting... I was guessing 12/2 was 1/2 inch wide. Long ago I did once
try to pull a 12/2 through a 1/2" EMT and while it can be done, that stuff
is very, very difficult to get around any sort of bend in a tube that tight.
Even if it is allowed you'd be hard pressed to have a good reason to go to
that kind of trouble, far easier to use single conductors. I imagine 12/3 is
even tougher.

You can pull 10/2 thru 1/2" PVC. Fortunately, it was _real_ short, without
any bends.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.