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Old 20-Apr-2016, 9:59 PM   #1
twaw
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Join Date: Oct 2015
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Possibly the dumbest question on grounding

I'd posted earlier about this but have run into an unanticipated development today, as I was running my final ground. To make a long story short, it's a 30' antenna, and I have to run my antenna ground into the house to the house panel ground bus. AD Tech had kindly advised me on this so I'm going with one of his recommended options.

But getting to the original single point of entry of the house service has proven to be harder than I thought (never buy a 200 year old house). It's a lot easier to run a new, more direct entry... let's call it Entry #2... BUT that's only about 1.5' away from my oil tank fill pipe, to the tank in the basement. BTW the closest point of the tank itself is only about 3' from the panel. And it will enter at ground level.

I'm almost certain that the panel is grounded to my 450' well, much better than a ground rod. The original existing panel ground wire exits just 2' from the tank fill pipe and 2' underground. So my new entry point is about the same place as the existing ground cable.

So here’s the dumb question: Is it a really, really bad idea make this new Entry #2 so close to the tank fill pipe... the lightning arcs to the oil filler and the tank, and, well... I'll have an extremely bad day.

Or, since the existing ground is practically the same distance, and even if I use the original entry which is about 8' from the fill pipe, the current's going to hit the panel and then the existing ground cable anyway, and will still pass within 2' of the fill pipe on it’s way to the well ground…?

The other thought I had, I could easily add some kind of "barrier" or shield between the ground wire and the oil fill pipe. Don't know if that would help at all, I mean, I know how powerful lightning is… or what material I would use... wood, flashing, sheet metal? OK, I'm clearly grasping at straws here.

The other possible concern with going to the original existing entry, it's is much further from the fill pipe at 8’, but it’s a longer run inside the basement and passes on top of a lot of wires, BX conduit, etc. to get to the panel. On the other hand, this new Entry #2 results in a much shorter run inside the basement to the panel ground, only about 4' total inside.

I may be splitting hairs, but I want to do it right. I'm more than willing to do the extra work to go to the original Entry if that’s worth the effort. Any thoughts are appreciated... thanks!

Last edited by twaw; 20-Apr-2016 at 10:22 PM.
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Old 21-Apr-2016, 1:05 AM   #2
ADTech
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At this point, contact your local AHJ with your situation, if there is one for your locale.

Keep in mind that the purpose of grounding an antenna is NOT to absorb a lighting strike (that's the province of a lightning protection system, quite a different animal), it's to drain off static so the antenna mast is less inviting to a strike and to protect against accidental energizing of the mast in the event of an accident.

If lightning were to hit the mast anyway, the whole grounding system is going to convert to plasma in a minute fraction of a second. Destruction will be extensive.
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Last edited by ADTech; 21-Apr-2016 at 1:11 AM.
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Old 21-Apr-2016, 2:27 AM   #3
rabbit73
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One August day several years ago, we had a very close strike with little time between the flash and the thunder. It took out my computer even though it was off, plugged into a good surge suppressor strip, which was also off, and connected to a 3-wire outlet properly grounded to the electrical panel ground.

Interestingly, the old Sony TV with a CRT picture tube in an adjacent room was on, but the colors were crazy. I turned the set off and then on again, and heard the normal loud "thunk" from the degausser; the colors were then OK. It seems that the EMP from the close strike had magnetized the metal shadow mask in the picture tube.

I now uplug the power strip when not using the computer.
Quote:
At this point, contact your local AHJ with your situation, if there is one for your locale.
Good advice from ADTech, since this is now your third thread stating your concern.
Quote:
Originally Posted by twaw View Post
My house has been hit by lightning before, lost a lot of electronics, so I really want to ground it properly... without going too crazy on cost. Plus I intend to move the antenna in a couple months another 70' to my nearby field for better reception, and will bond it with rods every 25', which seems to be the conventional wisdom.
If you intend to move it to the field, you need to do your research as if it were a ham (amateur radio) tower installation.

You also need to talk to a local electrician who can tell you if the local electrical inspector, who would be the AHJ (Authority Having Jurisdiction with the final say on the Code) is friendly or not.

Antenna System Bonding and Grounding Requirements
http://www.reeve.com/Documents/Artic...ents_Reeve.pdf

https://www.google.com/?gws_rd=ssl#q...ower+grounding
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Last edited by rabbit73; 21-Apr-2016 at 10:26 PM.
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Old 21-Apr-2016, 11:41 AM   #4
shoman94
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Is there any reason why one couldn't just install a new ground rod near the antenna location? I would think that having that line run into the house would be a mistake.

Last edited by shoman94; 21-Apr-2016 at 11:55 AM.
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Old 21-Apr-2016, 1:15 PM   #5
rickbb
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Multiple grounds when done properly are ok. The problem is doing them properly.

Some local codes don't allow them due to keeping them isolated from each other is more complex than it seems. And often ends up creating more problems than they solve.

It's better to have a single path to ground, it's just easier to maintain and safer.
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Old 21-Apr-2016, 1:30 PM   #6
ADTech
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Quote:
Originally Posted by shoman94 View Post
Is there any reason why one couldn't just install a new ground rod near the antenna location? I would think that having that line run into the house would be a mistake.
Multiple ground rods must still be bonded together per code.

Keeping ground lines outside is not a bad idea, it simply wasn't deemed important to the code writers (NFPA) and therefore is not a requirement. If the National Fire Protection Association didn't think it was important enough to specify otherwise , I'm not going to argue with them, especially when the code EXPLICITLY permits the practice. See NEC 810.21(G).
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Last edited by ADTech; 21-Apr-2016 at 1:34 PM.
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Old 21-Apr-2016, 10:48 PM   #7
rabbit73
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More lightning protection references from the ARRL:
http://www.arrl.org/lightning-protection
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