Bill writes:

Doug, Thank you, as always, for your thoughtful answers!

I normally space holes about 2"
apart, but there's no hard-and-fast rule about that.

Do you mean 2" between centers? Since "straight-up" is the best way to
exit my subpanel, I wish to be efficient. I've already planned 8 cables
coming out, with others likely to follow. Putting two 10-2 cables in a
3/4" hole and two 12-2 (or 14-2) cables in a 5/8" hole ought to be
efficient! I'll follow the same grouping rules threading the wires
through the wall studs. Lew Hodgett pointed out that threading three
10-2 cables through a 3/4" hole was definitely wrong. I would appreciate
knowing his point of view concerning this.

It's not clear from this, but do ensure that you never run mutiple
romex cables through a knockout on the subpanel. Once cable (with
appropriate clamp) per knockout.



Is there any problem with different gauge cables sharing the same hole
(I considered that the conduit on the lesser cable might not be adequate
to be next to a hotter cable)? Swingman (smartly) advised me not to do
anything I don't feel confident about--and this is a detail that makes
me hesitate.

Not a problem; assuming again that you're referring a hole in a framing
member, not a knockout in the panelbox.

scott