Grounding an attic antenna - AVS Forum
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post #1 of 9 Old 12-19-2002, 02:04 PM - Thread Starter
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I have an attic antenna and I am wondering what proper grounding is for attic antennas.

Should the mast be grounded? Does this "complete the circuit" in some way?

Should there be a ground block in the line?

Thanks in advance...

Jeff
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post #2 of 9 Old 12-19-2002, 04:13 PM
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jswclw -
I agree with jeffthurmont you don't need to ground it. Wouldn't hurt to run your coax through a lightning arrestor/ground block anyway if you have a good earth ground close by to tie it to. Might offer a little protection against high electric fields from nearby strikes. On a side note - it's usually good to ground masts and outdoor antennas. Lightning can/will strike them since they are usually highest point on roof. You want to shunt the high current directly to ground on the outside of the house, not let it go down your coax or parts of your house (starts fires). Grounding it won't attract lightning any more than the shield of the coax that's already running up there.
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post #3 of 9 Old 12-19-2002, 05:02 PM
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Hard say. The antenna-specific sections of the electrical code, sec. 810, are really for outside antennas. In the absence of specific guidelines, one is left with these sections of sec. 250-2, "General Requirements for Grounding and Bonding":


(b) Grounding of Electrical Equipment. Conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials. Where the electrical system is required to be grounded, these materials shall be connected together and to the supply system grounded conductor as specified by this article. Where the electrical system is not solidly grounded, these materials shall be connected together in a manner that establishes an effective path for fault current.

(c) Bonding of Electrically Conductive Materials and Other Equipment. Electrically conductive materials, such as metal water piping, metal gas piping, and structural steel members, that are likely to become energized shall be bonded as specified by this article to the supply system grounded conductor or, in the case of an ungrounded electrical system, to the electrical system grounded equipment, in a manner that establishes an effective path for fault current.

So, do you have to ground the mast? Probably not, although it's up to the local inspector? Is it a good idea? Yea, especially if you have alot of electrical wiring running around the attic as well.

You have a right to install OTA and dish antennas on property under your control.
See http://www.fcc.gov/mb/facts/otard.html
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post #4 of 9 Old 12-19-2002, 05:26 PM
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all of my attic antennas are grounded. all coax runs use grounding blocks. I would take a look at: http://www.lightningsafety.com/
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post #5 of 9 Old 12-19-2002, 06:50 PM
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Quote:
Quoted from www.orlandodigital.tv/Lightning.htm
Antennas In The Attic
If you think you are safer putting your antenna in the attic, think again. Lightning has traveled through a few thousand feet of air (which is a good insulator), two inches of plywood and shingles are not going to make any difference. Roofing nails will add a direct path through the roof anyway.

In the attic, the antenna is grounded through your equipment. This is the path all the static charge (and potentially lightning) will flow. There is always static charge, even when there are no storms around. Because the path is through your equipment, its a relatively high resistance path. This also means your HDTV receiver is having to drain any charge build up on the antenna through the house wiring.

The attic antenna needs to be grounded the same way as an antenna mounted outside.
I just took down my attic ant today (exchanging for another model) and was thinking about this. "You know, static discharge can still happen under this roof." When I put the new one in, I'll be grounding.

EDIT: MODERATORS: This seems to be a common misconception, perhaps its worthy of a FAQ or perma-note, for safety's sake.
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post #6 of 9 Old 12-19-2002, 06:54 PM
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My hot water heater is in my attic. Can I ground my antenna to the cold water inlet pipe for the water heater?
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post #7 of 9 Old 12-19-2002, 07:42 PM
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I would disagree with the statement that roofing materials offer no protection from lightning, otherwise people would not be safe in homes that have no attics - a large percentage of those located in parts of the country with high incidence of lightning. Building materials are good conductors when involved with such high voltages. Wood becomes a conductor, and that's why it often catches fire after a lightning strike. Anybody or anything is normally well-protected inside a structure. Any conductor coming into the structure (phone, electrical lines) can provide a path into the home however. That's why it's wise to stay away from them during a storm.

Static won't build up on an object unless it is well insulated (or an insulator itself). Perhaps if you mounted an antenna on nylon blocks and had the coax isolated with a balun with no leakage paths, you could get it to charge up. The path through equipment is not a high-resistance path, it is low resistance. The shield of coax cables normally is grounded to the equipment case, which has an earth safety ground attached. The coax and other stray paths prevent charges from building up on antennas, but you don't want these to be the paths when there is a lightning strike. That's why they should be well grounded with arrestors in the lead-ins.

Long runs of cables are also vulnerable to electromagnetic pulse from nearby strikes. Lightning may hit a nearby pole or tree, and the pulsed field couples onto the cable. This induces a large voltage spike on the equipment which can be high enough to damage it.

I agree, there are lots of misconceptions - including articles published in the paper and on the web. I also agree that the safe thing to do is to ground it if there is any concern that a hazardous voltage could come in contact with it ('it' could be about anything, except people of course).
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post #8 of 9 Old 12-19-2002, 09:08 PM
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Quote:
Originally posted by MurrayW
My hot water heater is in my attic. Can I ground my antenna to the cold water inlet pipe for the water heater?
Yes a cold water pipe is a suitible NEC ground.

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post #9 of 9 Old 12-19-2002, 11:01 PM
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Quote:
Originally posted by miatasm
Yes a cold water pipe is a suitible NEC ground.
It usually is. There are situations where at least part of the piping may be plastic or places in warm dry climates where the feed pipe is too shallow and the earth too dry. Make sure the cold water system is all metal and electrically bonded to the main building ground.

Pat

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