We are working on a grounding project in california for catv. we specialize in mdu's. Many times we have run into the situation where the only place to ground is a hundred or more feet away. In these cases we use a solid copper AWG# 6. Apparently you can go a lot further with a thicker wire. You might want to take a look at
www.cabetv.com. They are a well known authority for grounding in the cable industry. Good luck hope that helps