12 to get you 20 amps.
12/3 so that you'll have a white wire, for a neutral. In
case some 110 VAC equipment is needed up in the attic.
WG, so that there is a dedicated ground.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Tony Hwang" wrote in message
...

Hmmm,
12/3 and ground wire? How come?