Grounding Outside TV Antenna?

jaxoNovember 27, 2010

There is an antenna installed attached to the eaves of the house. It is not the highest point of the house since the roof peak is higher.

It looks really difficult to add grounding since there is concrete pavement below and instructions I read say you need to insert a metal rod 8ft into the soil.

Is it important to ground an antenna if it is not mounted at the highest point of a building?

If so, I will probably have to try find a smaller antenna that can fit in the attic since this one won't fit and it looks pretty impractical to ground this antenna.

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brickeyee

Lightning does not always strike the highest point, especially when a nice metallic object (good conductor) is nearby.

EVERY antenna (especially exterior ones) requires a solid ground.

Even an antenna in the attic should be grounded.

    Bookmark   November 27, 2010 at 9:04AM
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joed

An antenna doe NOT get a separate ground rod. It must tied to the building ground system.

    Bookmark   November 27, 2010 at 10:06AM
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brickeyee

"An antenna doe NOT get a separate ground rod. It must tied to the building ground system."

An antenna CAN have a separate ground rod, and often does.

The antenna ground is THEN tied to the NRC required grounding system.

The requirement is that all the ground rods be tied together, not that separate rods are prohibited.

    Bookmark   November 28, 2010 at 12:04PM
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alan_s_thefirst

"Even an antenna in the attic should be grounded"

Really? I didn't know that. I suppose lightning's not discriminating and can easily go through a roof. I do wonder though if an antenna inside an attic would be that much of an attractant.

    Bookmark   November 30, 2010 at 12:22AM
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Ron Natalie

I'm trying to figure out where to attach the #8 wire to my cell phone or my wifi laptop.

    Bookmark   November 30, 2010 at 8:19AM
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brickeyee

"I'm trying to figure out where to attach the #8 wire to my cell phone or my wifi laptop."

The grounding of antennas does not apply to portable equipment, just permanently mounted antennas.

If your laptop or cell are struck a solid ground will be the least of your problems.

    Bookmark   November 30, 2010 at 9:36AM
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Ron Natalie

The "grounding of antennas" doesn't exist in the code at all.

Outside antenna masts and supporting structures must be grounded. Discharge units for outside antennas must be grounded. There's no requirement to ground an antenna (and in fact, you don't want to do so).

    Bookmark   November 30, 2010 at 10:42AM
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brickeyee

"Outside antenna masts and supporting structures must be grounded. Discharge units for outside antennas must be grounded. There's no requirement to ground an antenna (and in fact, you don't want to do so). "

The "discharge unit" for an antenna provides a DC ground path for the antenna, while maintining a suitable impedance at the frequencies of interest to not interfere with the operation of an antenna.

The "discharge unit" IS grounding the antenna.

    Bookmark   November 30, 2010 at 3:35PM
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Ron Natalie

The discharge unit actually grounds the feedline. It's often located nowhere near the antenna itself. Many don't offer a DC path to ground either at low voltages.

Next weasel words from you to explain the statement that inside antennas need grounding?

    Bookmark   November 30, 2010 at 5:15PM
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brickeyee

"The discharge unit actually grounds the feedline. It's often located nowhere near the antenna itself. Many don't offer a DC path to ground either at low voltages. "

The discharge unit should be located at the base of an antenna mast or where the feed enters any structure, with as straight and sort a ground line to earth as possible.

If you have a discharge unit that is NOT providing ground continuity at DC you have a real hazard.

The charge that builds up on an antenna IS DC, and is caused by the voltage between a passing charged cloud and earth, or from simple air flow over the antenna itself.

Coils are used to provide the needed DC grounding while NOT shorting out radio frequencies desired.

Inside antennas while not covered under the NEC represent an excellent target for lightning.

The electrical insulation of a roof structure is NOTHING compared to the voltage of a lightning strike.

If the antenna can pick up signals, it can attract lightning.

    Bookmark   December 1, 2010 at 10:36AM
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Ron Natalie

Did you not read the part I said about "low voltages?" Some have a gas tube or even an airgap in them. They don't pass any thing until the static builds up to a certain potential.

    Bookmark   December 1, 2010 at 11:22AM
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Ron Natalie

By your argument, any metal inside the building would need to be grounded. There's nothing magic about an antenna. The code doesn't require any of this.

    Bookmark   December 1, 2010 at 11:23AM
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brickeyee

"By your argument, any metal inside the building would need to be grounded. There's nothing magic about an antenna. The code doesn't require any of this."

Most metal buildings are already grounded, so not a lot needs to be done.

The same applies to concrete buildings.

There are plenty of things the NEC does not cover, but other codes cover (and sometimes it is not actual code but installation instructions and techniques.

Antennas should be operated at ground potential to protect the equipment feeding them.
Spark gaps and discharge tubes have way to high a break-over to protect a receiver or transmitter from simple static build up.

You are correct, the NEC does not address all the issues, but any decent antenna installation should have grounding all the way to DC.

Unless you want to replace receiver front ends every time a thunder storm even goes past, let alone actual lightning strikes.

I worked in a building that did NOT have the correct rebar bonding, and we lost receiver after receiver, and a few transmitters along the way since we did not have a good ground on top of a 6 story building sitting out in what used to be farm fields.

We ended up running very large copper down wires (with very large radius bends) from the roof to earth.

After that we only lost a single antenna that took a direct hit (HF fiberglass whip) but the static build up that had been destroying equipment ended.

A row of new townhouses nearby took a hit also, and it destroyed the upper two floors of a 3 story end unit with damage throughout the unit before being brought under control.

We actually caught the strike (and subsequent fire) on a security camera.

An TV antenna had recently been installed in the attic, and the lightning followed the down line deep into the house.

The first floor TV was destroyed (as in blown apart) but the main fire damage was in the attic and second floor wall the antenna down line passed through.

    Bookmark   December 2, 2010 at 9:03AM
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tjcarita

brickeyee,

I just want to thank you for all the info about how important it is to ground your equipment.
I just grounded my TV antenna/mast and coax cable.
I drove an 8' rod into the ground as close to the mast as possible. I ran #6 copper between the new rod and the main house ground rod. I ran #10 copper from the mast to the new rod and then grounded the coax cable at the new rod using #10 wire to a coax ground block at point of entry into the house.
Thanks you for your post!

    Bookmark   May 16, 2012 at 7:47PM
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brickeyee

ronnatalie seems to think the NEC is the be all and and all of things electric.

It does cover antennas rather badly in Chapter 8, but is pretty far from a definitive document for this purpose.

    Bookmark   May 17, 2012 at 8:28AM
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ionized_gw

Grounding of rooftop TV antennas is of interest to me since I need to add one. Can anyone give me a link to a good reference that tells how to do it properly? How about some other resource that I might be able to check out of the library?

    Bookmark   May 17, 2012 at 10:17AM
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Ron Natalie

I never said the NEC is the be all and end all but it does cover the safety issues nicely. Also as a Commercial Radiotelephone operator, former broadcast engineer, and 30 years as an Extra class radio operator, I do know a thing or two about antennas. Grounding IS important, but grounding it CORRECTLY is more important, and the points I made about BRICKS errors are valid.

An external mast (and other metallic supports) should be hard grounded. I don't think you'll get any argument there. If you've bought a new antenna, it will already have the provision it requires to ground it and the instructions WILL tell you what is required for the antenna itself. And again, where the feedline enters the structure, an appropriate arrester for the type of feedline in use should be installed.

    Bookmark   May 17, 2012 at 10:23AM
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