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Originally Posted by Undertoad
How could one possibly know whether Comcast grounded their box correctly?
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I once sat for coffee with two Comcast installers who had just returned from training on this subject. Previously, no cable installers (apparently) had any idea what earthing (a 1930 technology) was about. As I explained these various points to them, the one kept saying, "So that is what they meant" and "So that is why we are suppose to do that". Like electricians, these concepts were completely foreign to most all installers.
The ground block on a cable wire is shown below. From this ground block (that is sometimes inside a gray box that had nothing but this ground block), a 10 AWG wire connects to an earth ground that you (the homeowner) must provide. If you did not provide this common earthing point, then Comcast, et al may install something inferior.
That earth ground, at minimum, must be a 10 foot copper clad rod (sold in any Home Depot or Lowes for about $10). Too often electricians or installers will even cut an 8 foot rod in half. That four foot rod is woefully insufficient earthing. A rod that is not solidly in earth (can be removed) is also disconnected from earth. Earthing concepts well proven before WWII and now made essential for every home are too often compromised by those who never learned how and why.
(BTW, those three light ground testers report nothing about earth ground.)
One rod is a major earthing improvement. Anything additional provides exponentially decreasing improvement. That Orange County Emergency Response center must be so reliable as to spend $thousands more on a 120 foot ground rod just to make the last 0.1% of lightning totally irrelevant. But a residential owner must, at minimum, install that earth ground rod with a 6 AWG bare copper wire that connects less than 10 feet to breaker box.
We have now identified both ends of the cable earthing wire. Returning to those Comcast installers' questions: let's say a cable connects only to a second floor TV. So they attach cable at second floor level, and then run an earthing wire from that cable down to an earth ground rod. They have just made that TV a target for damage. Incoming cable wire must attach at second floor level, drop down close to the common earthing electrode, make a less than 10 foot earthing connection, then rise up (separated from the 'drop down' wire) to attach to that second floor TV. Cable must attach short to earth ground before entering a building AND must separate its 'before earthing' section from 'after earthing' section. The 'less than 10 foot' rule is essential.
That wire from ground block to earthing electrode must have no sharp bends, no splices, must remain separated from all other earthing wires until they all meet at the earth ground, AND must remain completely separated from non-earthing wires. Too many installers want to make things neat. They nylon ty-wrap (bundle) wires together and make neat sharp bends. An old rule: neat often means an inferior installation. Neat can also make induced transient damage likely.
Pre-1990 buildings use water pipe as earth ground. No longer acceptable and not sufficient. Quality of an earth ground is not just in better conductivity. Distance from each incoming utility wire to that common earth ground is most important. That every incoming utility connects to the same earthing electrode is essential. Yes, that means even a satellite dish cable or TV antenna must first connect to earth ground before entering.
This is a ground block that would be inside that Comcast gray box. Earthing wire (often gray or green but in this case black) connects to this ground block: