RE: Wire Ampacity
A quick Google search on 'current capacity by wire gage' will lead to a
bunch of charts and to the Wikipedia entry that gives details on how wire
gage is measured/calculated and, if interested, provides a bunch of
equations used for the calculations.
Bottom line:  Use #10 for all small loads, #0 for everything else.  Just
kidding, I really don't use 50 amp fuses and #18 in everything, really I
don't.