I am replacing my 55 year old, 100 amp, 12 space outdoor service entrance panel with a new 20 space 200 amp outdoor panel. Since the new panel is 12" above the rim joist, I was thinking of using PVC emt elbows to get the branch circuits into the box. Code says I can run romex in conduit for short sections for protection.
How much NM cable for what size conduit (I have a 2" knockout and 9 @ 3/4" knockouts). And what about strain relief when the cable enters the panel?
This is what I'm trying to do. 
The new combo panel with underground service will be just to the left of this panel. There is a 6-3 cloth covered romex (soon to be replaced) in the large conduit. How do I get the other romex circuits into the new box?
Best Answer
For conduit fill calculations you have to treat romex/NM as a ROUND wire of the same size as its largest dimension (ie, the long axis of the oval.) Oddly enough this means that 14-2 is larger than 14-3 for conduit fill. As @SpeedyPetey notes nipple (less than 24") fill is 60%, not 40%, and is a LOT of wire to get into a conduit; but I don't think that's the major issue here if NEC compliance is a desired upgrade. The wire type and location is the main issue.
NM cannot be run in exterior/underground conduit since it is not rated for wet locations. With an outside service box that alone might mean you can't do this and meet code - at which point you'll need a major junction box or a lot of minor junction boxes inside, and some wet-location-rated wire until you are inside.
(And now that I've seen the pictures...)
My understanding of NEC (which does not seem to have been particularly involved in your current service, with exposed NM running outside) is that you would have to run a wet-rated wire (THW, XHHW, etc.) until you get inside the house, where you would connect to the interior type wire you currently have exposed to weather and sunlight. NEC defines (and reality frequently confirms) all exterior conduit as a wet location.