I'm in the process of getting the parts to install an electric fence.
If I use 17 ga galvanized electric fence wire with green metal posts
(and insulators of course), how far apart can I space the posts?

We did it by trial and error. Since we keep expanding the protected area, we
put in posts that just pound into the ground and they have to be no more than
10' to 20' apart and the wire does sag. With permanent posts, you could
probably stretch the wire pretty tight. In Several spots we take advantage of
trees and attach insulators to them.

Dave
http://members.tripod.com/~VideoDave