I have put off installing a transfer switch because the cable will need to
be run the length of the house (all those joists to drill through) and the
expense.
Well, I found a half price 5000w switch at HD and a half price right angle
drill at Ebay, so I am going to do it; but what cable size.

I have a 13a genny that satisfies all my needs. It would only require 14/2.
But as long as I am doing it, I might as well install a 12/3, as the next
owner might be more demanding. The cable won't be that much more, or be
that much harder to use. However, the 12/3 is only good to 4800w, and the
switch is 5000w. Would those lousy 200w make any real difference?
Obviously they would need a 5000w genny, and even then it would only be
above 4800w for very short and rare instances.
I really don't want to use 10/3. It is expensive and hard to work with, and
will require a significantly larger hole in the joists. Does code get
involved here? Can I simply say that it is only for use with 4000w and
smaller generators? I have no intention of ever going above 1600w, and
expect to live here for the next 10 years at least.
Thanks.