If you use an exterior mounted television or radio antenna you should take steps to protect your TV and home from being damaged by lightning.I do not claim to be an expert in this field, however I have gone to the trouble to find articles on the Internet by several people who are, and I have taken their advise with very good results. At the bottom of this page you will find links to several "expert" sites on this subject.
Protection for a TV antenna which is located on a roof should be at three points:
1) Ground Connections at the Antenna The antenna, mast and lead in wires (as well as control wires for the rotator or similar equipment) should have a ground routed via the shortest possible path, without sharp bends or kinks to a ground rod which is connected to the main earth ground for the home electrical system.
2) At The Entrance to the House The antenna coax should enter the house as near as possible to where the telephone or cable TV wires enter (usually very near the electrical service entrance). This is called a single point of entry. All data and control wires should be grounded at this point with the shortest most direct conductor possible to the system ground rods.
3) At The Television A high quality surge protection device that protects both the power supply and the antenna wires should be used at all televisions connected to the antenna.
TV and Radio Tower Grounding
The antenna and mast should be properly connected (bonded) to at least one 8-foot ground rod that is located as close as possible (preferably within inches) to the mast. If the mast does not go to the ground (as in a roof-mounted antenna) then the ground wire should run as directly as possible straight down to the ground rod. The coax wire should also run directly down from the antenna to the vicinity of the ground rod where the coax shield is connected (by way of a ground block or other method) to the main ground wire.
It is very important that the coax (or control wires) run straight down as close as possible to the earth and the shield ground connection before being routed into the house. You must do this even if this means that you will have to run the wire a long way back up to a second or third floor room where the TV is located. It is also advisable to ground the coax shield near the top of the antenna mast, but it is critical to do so at the base.
You might be able to get away with using the mast as the grounding conductor especially if it is a single piece of metal. However, if you are using some kind of "extend-a-mast" then you should probably bond the pieces together by running a #4 ground wire from the top of the mast all the way to the ground rod. What you are trying to accomplish is to supply the lightning with a very good path directly to ground that does not lead through your wiring. In either case the connection between the antenna mast and the ground rod needs to be robust and long lasting.
At the House
After your coax and control wires (if any) are grounded at the base of the antenna, they should be routed into the house at the same place that the telephone wires enter. At this location on the outside of the house the coax shield should be grounded again in the same manner as at the base of the antenna mast or connected to a lightning arrestor. However, the entrance point ground should be connected as directly as possible to the ground wire leading to the main ground rod(s) for the electrical service. If you look you will probably see that the telephone and cable lines are connected to the system ground as described using a ground block, and a split bolt ground clamp at the system ground wire. You might even be able to utilize existing hardware to make your connections. This is also where you would put a rotator/control line protection device to protect the coax wire or rotator control wires.
At The Television
At the TV You should use a high quality surge protector which is designed to protect not only the power supply but also the coax wire. The surge protector must be plugged into a grounded outlet or connected to the main system ground by way of a grounding adapter for it to function. Note: Don't plug your surge protector into a GFCI protected outlet that is on an ungrounded two wire system or it will not work! Quality surge protectors are rated in joules (higher numbers are better) and will have a warranty covering connected equipment.
Use electrically conductive grease (such as ideal brand noalox or equivalent) at all bonding connections, especially if there will be aluminum or any dissimilar metals being connected.
Keep your ground wires as short and direct as possible. The bigger they are the better they will perform, but keeping them short is even more of a factor.
Use ground rods that are suitable to your local soil conditions. If you have highly conductive soil then one 8' ground rod will probably be enough, but if you have dry sandy soil you might need more than one. Whatever local codes require for home electrical system grounds should be fine. Ask at your local electrical contractor supply store where you buy your ground rod.
Always connect the antenna ground rod to the main system ground using at least a #6 copper wire. Relying on the earth to connect them will not work. You want a single point ground even if you have multiple ground rods. Failure to do this will usually result in a ground loop which will plague you with noise, snow, hum, and all manner of puzzling electrical problems.
Use ground rods, don't try to ground your system to a water or gas line.
Don't run your ground wires into or through the house, basement or crawl space. Keep all of the ground elements, wires, rods, bulkheads and other connections outside.
Drive your ground rod as close as possible to the base of the antenna mast, but you want it to be in soil that will be wet as often as possible so don't place it where it will be too protected by the overhang of the house.
I installed a TV antenna on my own house about a year ago using these techniques and so far we haven't had any problems whatsoever despite the fact that we live on the very top of the highest hill around. We live in middle Tennessee and lightning storms are a regular fact of life here, but I have complete confidence in this system after living with it for a year.
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