Ham Radio Equipment (12-30-99)
 

Mike, I have a ham radio antenna setting on top of a 50-foot mast outside my house. There is a rotator device for changing the direction of the antenna. The electrical service is on the opposite side of the house (about 75 feet from antenna). There is a metal rod driven into the ground next to the antenna mast. There are 2 ground clamp fittings connecting a No. 10 wire to the rod and antenna mast. I don't see a ground wire on the cable running into the house from the antenna or on the cable from the rotator motor. In addition, both the antenna cable and rotator motor cable are sleeved underground in black plastic pipe and run exposed up the outside wall and directly into the eave of the house. Could you tell me how to properly ground this system to get good lightning protection?

Response No. 1.

To properly protect from lightening and to ensure a proper ground path for transmitting, I recommend a #10 wire be independently from the ground rod directly to a Ground Copper 12" x 2"" Buss Bar located in your shack. From "common" the Ground Buss bar, connect a #10 directly to the Power Supply Lug called "Ground. Yes, on high-end power supplies a ground Lug will be available in addition to the Negative and Positive Poles. Connect the ground of the Rotator Case shield also to the Ground Buss Bar. Refer to FCC Part 97 and NEC 99 Code on Antenna Grounding.

Mike Van Voorhis, N8VIQ

Response No. 2.

Mike: I have used the following procedure to ground HAM radio towers for many years and have never encountered any problems with lightning.

Drive three six to ten foot ground rods (copper coated) in a triangle shape around the base of the antenna. Connect all three together, preferably with copper weld, and then run a cable up the tower to a lightning rod. Connect the lightning rod, cable, and tower together at the highest point possible. The cable (grounding conductor) should be at least AWG#2. The size of the ground rods is of course predicated on the ground resistance. This method is preferred to using the tower and its foundation as the ground rod for various reasons. One is the fact that many towers pose a high resistance to ground, and much of the hardware and conductors hanging on them provide an easier path to ground. The independent cable and ground rods serve to shunt the lightning strike to ground.

Hal Seeley, HjsMind@aol.com

Response No. 3

Mike a good place to start for grounding is http://www.polyphaser.com/menu.html. This site has many technical articles on grounding including ham radio installations. They also sell the specialized hardware need for grounding coax, and rotator cables. The main thing to remember is that lightning "runs down hill. I used to have a Polyphaser book that listed products and suggested installation drawings, but I loaned it out so many times that it forgot the way home!

Elard Haden, ehaden@sterlington.angus.com

Response No. 4

See Section 810-51 in the NEC, which refers to Section 810-21 for grounding requirements of Ham radio stations.

Will Barnett barnett@ci.gresham.or.us

Response No. 5

I have checked with my friends at Hart & Associates Inc. in Phoenix. Arizona (They specialize in lightning protection). They advise setting up a ground ring around the base of the antenna tower. To do this you will need to dig a trench around the entire base of the tower. The ground ring should be 2' deep and extend out 5' in all directions from the tower. You will need to run at least a 3/0 bare copper in the bottom of the trench, and attach each leg of the tower to the ring in the bottom of the trench. These leg jumpers
should be as straight and short as possible. A good quality mechanical is acceptable to attach the jumpers to the legs, however to attach the jumpers to the ring a process known as exothermic welding is the preferred method for the underground splices. If you are not familiar with this process, it should not be attempted by untrained persons, as it can be extremely dangerous. Unfortunately, no ground ring can completely guarantee protection
against lightning damage. However, a good ground ring is definitely worth the trouble of installing. It will protect against most lightning strikes. I would suggest that you contact a contractor in your area that specializes in this type of protection, to insure that the system is the correct size to protect your equipment.

Mwhite2690@aol.com

Response No. 6

Mike, regarding the Ham antenna question, from the 1999 code: Of course, Article 810 applies directly to this situation, 810-15 - Masts and metal structures SHALL be grounded 810-21 - with copper, aluminum, copper clad steel, bronze, or other corrosion resistant materials. (aluminum or copper clad steel shall not be used in contact with masonry or within 18" of earth) AND shall be attached to:

1. Building or structure grounding system

2. Interior metal water pipe

3. External means as provided for CCTV, etc.

4. Metal service raceway

5. Electrical service can or

6. Water pipe ground

If no other means available, you may drive your own ground rod. Note: make certain you run the ground as straight as possible, if not, you create a "choke" coil which will not dissipate a static charge and makes a high impedance ground.

Wire must be at least a #10 copper. Failure to ground your inside station equipment will possibly introduce high RF into your "shack" (operating position). This is usually accomplished by driving a ground rod outside your house and attaching the frames of the equipment to it. Please note this is acceptable ONLY IF you attach that ground rod to the service ground by at least a #6 copper conductor, for noise purposes, do not do this inside the panel, but at the rod or pipe.

For the system described, run a #10 copper through the plastic pipe attach to the mast ground rod and the service ground rod, or pipe. Run at least a #10 copper (I use #6) from your equipment inside the house, to a driven ground rod, and jumper it (with at least a #6) to the service ground. This prevents your electrical system from introducing "noise" into your conversations - the last thing you want is your wife's hairdryer to overrun your conversation with Japan!!!!

Add an antenna discharge unit in you lead in conductor (outside the house, please), as
required by 810-20 and 810-57 and you will be code legal and ready to operate safely, with little harm from most lightning situations. The discharge unit is available from most ham outlets such as "Radio Works, and "Ham Radio Outlet.

I still remove my antenna leads from my radios during most thunderstorms; I don't want thousands of dollars of equipment ruined by one quick static charge.

73's and Good DX, George Corron - AF4JH

Response No. 7

Ground rods are installed with resistance tests not to exceed 5 ohms. The power and coax lines should be routed through steel conduit. This will act as a choke to help prevent lighting from traveling into the house. Both lines should have lighting arresters on them. The coax when not in use should be disconnected from the radio to protect it and connected to a ground buss in the ham shack. This ground buss should have a separate copper conductor to a separate ground rod right outside the ham shack. With a #2
copper, wire welded to the ground rods, tower, and conduit. This includes two welded #2 copper ground tails off the tower. All ground leads should be headed in a down direction with a minimum of 8" radius on the bends.

Your mechanical ground connections will fail over time its just a matter of time.
Ed Siegenthaler, Erie3694@aol.com

Construction Manager Cellular Towers

 

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