grounded cause of ground

snooperloop · 11-Mar-2015, 9:28 PM

Greetings to all.. I hope from my quest to find a concrete answer you might help me with your knowledge.

It seems no matter where I search the internet (including this forum) I will see a question asked about grounding the antenna through the attic .. This usually has a few follow ups saying it is perfectly legal and that a ground is only to bleed off static not prevent lightening strikes and how no matter where ground runs it will be vaporized in an instant regardless... basically the (it don't matter where ground runs if lightning strikes your setup dude you will have a mess).

Then typically the very next responder will say (noway should you ever run a ground through your house are you crazy? why give lightening a path in?)

Not being an electrician or great on the laws of physics and electricity honestly they BOTH MAKE GREAT POINTS lol.

But alas here I ask... to get a consensus on what you all might do given the situation.

1. Logical line of sight point is to mount antenna to chimney.. Due to roof design having ZERO gables though I have no where to run the ground to the electrical ground. I could tuck the 10awg ground wire under the shingles or just run it straight down the roof.. Shingle tucking Yes.. exposed across shingles just too tacky for wife.

2. Mast on side of house where electrical ground is located. This I do not really care to do as due to a 2 story house directly behind that side of house and direction of broadcasts This would need to be a 30 foot mast.

3. Mount the antenna right at the bottom roof edge on OPPOSITE side of the house... Has line of sight.. But I would need to run a second grounding rod and run 6awg wire 100 feel along bottom of house to bond to electrical ground.

Best signal is going to be chimney . I just worry as this does still have about a 60 foot ground run. Which I have read is cautioned against having that long.

GroundUrMast · 11-Mar-2015, 11:06 PM

I would start by proving the location(s) that provides reliable reception. There's no point in mounting a receiving antenna where it can't receive a usable signal. If there are several good choices, then select the location that offers the best access for running coax and the grounding conductor.

There's a fair bit of confusion about the length of grounding conductor that is either 'ideal' or 'allowed'. Unless I've missed it, there is no specific language in Article 810 of the NEC that specifies or limits the length of either the mast bonding/grounding conductor or the coax grounding block bonding/grounding conductor.

I advocate for treating the mast bonding/grounding as a separate connection that should not be shared with any other bonding/grounding connection, including the coax bonding/grounding. If the mast bonding/grounding conductor is quite long, it can be expected to have significant voltage drop along it's length if fault current is present. By keeping the mast bonding/grounding isolated from other systems or sub-systems, you avoid a fault current (and the resultant I*R voltage drop) in the mast bonding conductor from being able to cause current to flow in other parts of the home electrical system.

Article 810 of the NEC allows you to run any length of bonding/grounding conductor between the mast and your electrical service grounding system, using wire no smaller in diameter than #10 AWG copper (or specific equivalents listed in 810.21 (H)) . You may choose to add a ground rod to serve the antenna system... But you can also choose not to. If you opt to add a ground rod, the NEC requires that it be bonded to the existing electrical service grounding system with #6AWG copper and approved connectors. I've come to the conclusion that most installations would cost more and have no added protection if you opt to add a ground rod.

Though the NEC does not clearly prohibit sharing a bonding/grounding conductor between the mast and coax, it's my opinion that the coax grounding block should be treated as a separate sub-system of the antenna system. In an effort to minimize the effect of voltage drop when fault current is present on the coax, the ideal length of bonding/grounding conductor would be zero. In practice, placing the grounding block close to the electrical service grounding system connection will minimize the length of conductor run. This placement should also reduce or eliminate the need for bends in the bonding/grounding conductor that runs between the coax ground block and electrical service grounding system. 'Ten feet or less' is an oft' repeated 'rule of thumb' but there is no specification in article 810 of the NEC.

Artical 810.21 (G) specifically allows for the bonding/grounding conductor to be run inside the building... I choose not to if at all possible. I would spend additional time and money to avoid building a path for fault current into my home from an outside source.

The goal of bonding/grounding an antenna system is first and foremost to guard against large voltage differences from appearing between any part of the antenna system and other conductive objects that a person could come in contact with (i.e. protecting humans against electrical shock.) It's possible that you'll get other benefits from bonding/grounding, but they're secondary.