This is what the NEC meant by a static discharge unit when it was alluded to in the 1993 revision.
http://cgi.ebay.com/TV-FM-Antenna-30...item27b9ad5523
As I recall, that term was dropped from the code starting with the 1996 revision and didn't get re-inserted into the NEC until the 2005 revision, at which time it became a common topic of conversation at installer's conferences, as it was undefined. Somewhere, I have a copy of the 2008 version, but I'm pretty sure without looking it up that it now explicitly says that a block that enables grounding of the outer conductor satisfies that downlead grounding requirement.
There was, and probably still is, a bloated-shaped grounding block that has a gas filled spark gap chamber that facilitates static discharge of the center conductor. I bought a dozen of them back in the late 1990s but never used one. I suspect that its internal design was similar to whatever the old twin lead units like the one I linked above had inside them.
Update: lots of manufacturers and distributors are still making and selling it under the part number GRB-AR and calling it a gas tube, lightning arresting grounding block. Here is an old picture of it from a "cable museum" website
http://theoldcatvequipmentmuseum.org.../index.html#GB
The most recent few revisions of the code permit the mast to be grounded by 8 gauge aluminum, 10 gauge copper, or 17 gauge copper clad steel. For several fairly recent revisions, the code had specified that the outer conductor of the downleads had to be grounded with copper wire that was approximately equal in current carrying capability to the cable's outer conductor, which was not defined by the code or by any authority. One electrical inspector who was a ballbuster made me ground an outer conductor with 6 gauge copper. He said that while it probably had less current carrying capability than did the outer conductor, he could rationalize allowing it because, since supplementary rods could be bonded with 6 gauge wire, it would make no sense to require that the connection to that rod be any larger than the bonding jumper.
Quote:
HOW TO PROVIDE LIGHTNING PROTECTION FOR YOUR TV ANTENNA AND SET
(For outside mount)
... Lead-in wire from antenna to lightning arrestor and mast ground wire should be secured to house with stand-off insulators, spaced from four to six feet apart.
The standoff requirement was dropped long ago. Back then, we used to actually twist the flat lead once every few feet to enhance the effectiveness of "common mode rejection." Though not mentioned in the above excerpt but appearing in other, outdated NEC versions cited elsewhere on the internet, the code no longer requires that rotors be wired with flat cables with the outer two conductors grounded, either.
Quote:
In the case of a “ground up” antenna installation, it may not be necessary to ground the mast if the mast extends four or more feet into the earth. Consult your TV service man for proper depth in your area.
I think that exception was dropped because the conductivity of the contact surface of a "planted" mast could not be relied upon, as it might be painted, or might be ferric and rust, can't be inspected, etc.
If someone has the 2008 NEC handy, they may find that there is now a stipulated gauge for grounding the outer conductor that is maybe 10 or 12 gauge. I know a lot of franchised cable companies have long used 12 gauge insulated for that purpose.
One electrician once told me that if you do use insulated ground wire, you have to use green. I work for myself and always use black, just because I consider it to be a little less of an eyesore when run in an eave of white vinyl siding.
While all revisions of the code I have read stipulated that if a ground rod is installed to facilitate mast grounding it had to be 8' in length, I have never seen a minimum dimension for a rod driven to supplement the coax outer conductor grounding. There is a difference between "Supplemental" and "Supplementary" ground rods. One is used to complete the formation of the ground electrode when the soil conductivity is poor and must meet specs identical to those of the main ground electrode, whereas the other is added to the system rather arbitrarily to make a path to earth a little more direct. In 800s subsections for telephone wiring, for example, the code says (or said) that you could use a five foot rod in that application. Hughes satellite internet installers have long been instructed to use five foot rods, which Hughes furnished.
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