Grounding an antenna

tommymc

DTVUSA Jr. Member
#1
Can somebody explain the benefits antenna grounding in simple terms? I've seen the diagrams, I know how to do it. I've been using an ungrounded roof mount for over twenty years. When there is a lightening storm, we disconnect the co-ax cable. There have been lightening strikes within a few hundred feet of the house causing us to lose garage door openers and CFL's. I used to just kill the garage's breaker during lightening, but after losing the second garage door opener, somebody pointed out that the breaker is still grounded....unplugging the unit entirely makes it "invisible" to the lightening. Are we just lucky that the antenna was never struck, or is it invisible if it's unplugged?

My understanding of lightening is that it's looking for ground. Doesn't grounding the antenna make it a big lightening rod......putting a target on the roof? If a grounded antenna is struck, will the entire billion volts discharge down the tiny ground cable, or does the TV get zapped anyway? The co-ax grounding block is downstream from from the antenna mounted pre-amp so that's a goner right?

I know it's code...I just want to understand how this works....thanks.
 

Don_M

DTVUSA Member
#2
The physics behind lightning is somewhat similar to that of gravity acting upon water in that both seek the path of least resistance: lightning to ground, and water to the lowest point. Lightning strikes happen because the static charge -- the difference in electrical potential between a cloud and the ground (or objects attached to the ground, such as buildings, trees, lightning rods or antennas -- builds up to dangerous levels. A good grounding system offers static energy a clear, continuous path toward ground, where it wants to go anyway. It dissipates the static charge before it has a chance to approach lightning-stroke potential in the first place. To continue with the water analogy, a grounding system is a bit like the vent in your bathtub -- it also acts as an emergency drain that delays flooding if someone forgets to shut off the tap.

Unplugging the coax feedline is highly recommended during electrical storms, as is unplugging the TV from the wall outlet. These are the only sure-fire ways of protecting the circuitry from static-discharge damage. BUT: Unlike the garage-door opener, the antenna is most certainly not invisible to lightning when unplugged. Since the antenna is otherwise ungrounded, there are circumstances under which the unplugged coax cable could act as a grounding line, resulting in a discharge within the home! So, yes, you have been lucky over these many years -- extremely lucky.

Remember that there's no such thing as absolute protection from a lightning strike. The antenna, grounding system and electronics can still be destroyed by one good discharge. (It doesn't even need to be a dramatic storm. I also lost a garage-door opener once to static discharge. Lightning wasn't visible and thunder was alll but inaudible at the time. IIRC, the nearest thunderstorm cell was about 30 miles away.) The good news is that replacing these components is a lot easier and cheaper than replacing the whole house!
 

tommymc

DTVUSA Jr. Member
#3
Thanks Don...So you're saying that wind etc creates a static charge in the antenna which attracts lightening? So the ground wire prevents the static charge...and in case of a lightening strike it gives the charge a path to ground outside of the house.
 

SWHouston

Moderator
Staff member
#4
OTA System Grounding Components

tommymc,

When you start this, here's some items you may consider...

Ground Block*:
OR Surge Protector (both not necessary)
System Surge Protector*:
Wire (30’):
Some Locals require a minimum size of 8 gauge wire for Grounding. (check your local codes)
And one of the following:
Ground Rod (4’):
(for exterior Grounding)
Ground Rod Clamp:
(for above Rod)
Pipe Clamp:
(Exterior or Attic)
Copper Clamp:
(For clamping on a Metal Beam/Structure/RV)

Above required for basic Mount/Mast grounding (30’).
The above Surge Protector is different from one listed below**.
Use Surge Protector for enhanced component protection.
.* = Incretion of these components, will require the use of an additional piece of Coaxial Cable,
OR, the existing Cable can be cut, and two additional “F” Connectors installed, PER ITEM.

Component Surge Protector**:
(End of Line/at Component)

One other thing, if I may...
If you're just grounding an Attic Antenna, then the Ground Block will do nicely, and no problem running the wire through your Attic to a Metal Cold Water Pipe.

HOWEVER !!!
IF you're grounding/protecting an Antenna which is monuted on your Rooftop...
KEEP ALL OF THE BLOCKS* AND GROUND WIRE OUTSIDE OF THE STRUCTURE !!!

When Lightning hits a system, there could be some sparks popping off in various directions, and you DON'T want them flying around inside. Just a word to the wise.

Have a good Day ! :brick:
S.W.
 
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FOX TV

Contributor
#5
Can somebody explain the benefits antenna grounding in simple terms? I've seen the diagrams, I know how to do it. I've been using an ungrounded roof mount for over twenty years. When there is a lightening storm, we disconnect the co-ax cable. There have been lightening strikes within a few hundred feet of the house causing us to lose garage door openers and CFL's. I used to just kill the garage's breaker during lightening, but after losing the second garage door opener, somebody pointed out that the breaker is still grounded....unplugging the unit entirely makes it "invisible" to the lightening. Are we just lucky that the antenna was never struck, or is it invisible if it's unplugged?

My understanding of lightening is that it's looking for ground. Doesn't grounding the antenna make it a big lightening rod......putting a target on the roof? If a grounded antenna is struck, will the entire billion volts discharge down the tiny ground cable, or does the TV get zapped anyway? The co-ax grounding block is downstream from from the antenna mounted pre-amp so that's a goner right?

I know it's code...I just want to understand how this works....thanks.
Proper grounding and lightning protection required

A properly installed outdoor antenna requires adequate grounding and lightning protection, and a lot of antennas are not considered as being properly installed if this area of extreme importance is ignored. First of all, make sure all of your reception gear is plugged into a high quality surge protector, preferably one that's guaranteed for at least the amount of your equipment replacement costs. There are surge protector models available that allow you to connect your coaxial cable to it for additional protection.

You also need to make sure that it is plugged into a properly wired and grounded receptacle. Any receptacle that does not have the third or center-grounding prong is not properly wired or grounded, and they will not protect your equipment, as surge suppressors use the third grounded prong of the receptacle to send voltage surges to ground.

Attached to this post is the basic grounding diagram suggested by the National Electrical Code in section 810-20 regarding proper antenna grounding. You can sometimes find the exact applicable up to date code at your local library.

You should also be aware that a coaxial cable grounding block is not adequate lightning protection, as it only grounds the outer braid of the coax and not the center conductor. A plasma gas antenna discharge device is the best lightning protection method currently available. The high voltage of a lightning strike causes the plasma gas to ionize, thus providing a discharge path to ground, even for the center conductor.

Even though a good gas discharge device can be rather pricey, so is a 52 inch Plasma TV. This is the best method available to protect your expensive digital TV, and any other connected components such as stereo receivers or audio amplifiers.

These are normally commercial devices, and not really easy for the consumer to find. You may find one available at http://www.pasternack.com, but they are very proud of their products price wise. If your antenna is grounded, in theory, it constantly bleeds atmospheric voltage to ground. The natural atmospheric voltage potential difference always exists between the atmosphere and the Earth.

When thunderstorms develop, the clouds act as a large capacitor by building a charge large enough to overcome the dielectric properties of the air around them, and then they discharge with hundreds of thousands of volts or more, as these extreme voltage levels are required to overcome the dielectric properties of the atmosphere, and the plasma gas antenna discharge units work on a similar principal.

I am glad you asked this question for I have not seen one comment on proper antenna grounding on all of these antenna related posts. This is a very important issue that should not be ignored.
 
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