Mike Holt, a widely recognized expert on the topic of the National Electrical Code, has made the portion of his guide that deals with the NEC's Chapter 8 available for free download on his website.
The full guide is entitled "Mike Holt's Illustrated Guide to Understanding the National Electrical Code, Volume 2." The chapter of his guide that can be accessed for free is titled "Communications Systems." It is 38 pages in length and available as a PDF (approximately 6 MB) for viewing or downloading from the website mikeholt.com.
The guide illustrates and explains the 2008 NEC. A 2011 edition of the NEC has since been published. Even so, the 2008 version remains in effect in many jurisdictions that adopted it into their building codes and have not yet updated to the 2011 edition.
You may also be interested in reading these articles, authored by Stanley Kaufman, Ph.D. and previously published in Cabling Installation & Maintenance magazine, that describe changes made from the 2008 NEC to the 2011 NEC.