10 or 12 is the wire size, 2 or 3 the number of conductors. All Romex type
cable has a ground which is not referenced as an "official: conductor. 10/3
cable has 3 10awg power carrying conductors and a ground. The 3 conductors
are white (neutral) Black and Red (hots) and is used in balanced 240/120
volt circuits (120 from each hot to neutral, 240 across the hots) 10/2 has
a white and black and is used in 120volt circuits only.

You have 2 issues in wiring a shop, the size of the conductors and the type
of circuits.

Size your conductors based on length of run and branch current rating. 12
awg is standard for 20amp, but I would use 10 for longer runs.

When I designed my shop I ran both general purpose 120volt, 20 namp
circuits and 240volt 20 amp circuits around the shop. the 120s are for the
light stuff, the 240s for larger tools like my lathe, DC etc.

I also ran several dedicated 240volt 50amp or larger circuits for stuff
like welders, compressors etc (Yes, I'm a turncoat, I also work metal!!)

Fri, 10 Aug 2007 14:19:22 -0700, wrote:

In recent posts I have heard mention of 12/2 and 10/2 wire, as well as
12/3 and 10/3 wire. What is the difference and what would you wire a
new shop with?

I assume the 12/2 and 10/2 mean with ground.? What is the extra wire
in the 12/3 and 10/3 for? Is that for wiring 220V?

Jim