Amateur Radio Grounding to Protect Against Lightning

Disclaimer - This material is presented here to help others, who have never put up a tower before, as was my situation. It is a collection of information which I obtained from many very helpful people. Please do not hold any of us responsible for problems that you encounter as a result of reading this information.

Introduction

When I started the Infernal Tower Project, I knew absolutely nothing about grounding and so my initial grounds were inadequate. Based on suggestions and what I have read, I have made several changes, and will finish the job when weather permits.Thanks to the following Amateur Radio Operators who have personal experience with grounding and lightning and have kindly shared this information with me. I have edited the material slightly.

Dean Denter VA3CDD wrote the following ....

As far as grounding systems are concerned, I looked at the PolyPhaser information, and did a lot of reading on the net (any of the grounding articles by Gary Coffman are highly recommended).

(On my tower) I have a 10' U shaped ground around the base of the tower buried about 1' below grade with 4 6' ground rods (.5" copper pipe). The U ground is 4" wide, .025" thick copper strap, and is joined to the legs of the tower by 2" wide X .025" thick copper strap with is bolted to the tower legs using 3 #10 stainless steel bolts (per leg) with a piece of stainless strapping between the galvanized leg and the copper strap to reduce the dissimilar metals problems. There a 4 ground radials joined to the U shaped ground, each is at least 25' long and made from 1.5" wide X .010" thick copper strapping buried about 4-8" below grade with 3 6' copper ground rods (.5" copper pipe) along the length. All copper strapping is from Cohens, and pipes are from Home Depot. The copper pipe is joined to the strapping by slitting the end of the pipe, flattening it, then clamping the strapping between the 2 flattened ends and holding it in place with 2 brass bolts put through holes drilled in the flattened ends.

There were some problems with pounding the rods in (I also have lots of rock here, and the bedrock is only about 18" below grade), so some rods went in at an angle and others were cut in half with 2 short rods used at half the interval rather than 1 longer one used at proper 2 rod length intervals.

The ground system is joined to the house electrical ground using #6 bare copper wire. Given the number of thunderstorms I've seen roll through here over the last 3 years I've lived here, I'd consider this ground system barely adequate, possibly a little undersized, but then I'm paranoid about lightning (I've had towers hit).

Josh Kelly (N0NPI) writes....

I'm not sure how much lightning you get in your area, but here in Northern Iowa we get hit hard. The way I do grounding is to put in a minimum of three 8' rods at the tower base, one for each leg. I then like to run AWG2 stranded bare copper wire about 16 feet to another rod, for a total of 6 rods on the tower. The house electrical, telephone, Cable TV, and water lines should all be connected to this ground system (that is code here in the States). The shack ground should also be connected to this ground system. You want all equipment to be at the same potential if lighting does strike, having two grounds will not accomplish this, as the ground potential will raise when lightning strikes the tower (or power line etc.) If the shack is on a seperate grounding system it will be at a different voltage potential allowing current to flow through your equipment and causing damage.

This is the way we have grounded the commercial sites I have worked at, both Cellular phone and a large 600 meter TV broadcast tower.

For some excellent info on Lightning Protection visit http://www.polyphaser.com/ppc_technical.asp You will find an article on Ham Radio Station Protection in their Technical Information section.

With Respect to the Infernal Tower: Try bonding to the wells, but keep in mind that lightning may see those long well casings being fairly inductive, but it would probably still be helpful. Consider putting in rods every 16 feet or so and use bare copper when bonding to the wells. We used 30' well casing for grounds at cellular sites, and nothing else. It didn't work (too inductive?). Later (after I left that company) they added lots more grounding with multiple ground rods and bare radials and were lightning free this summer at one site that I used to visit 10-15 times a summer for lightning problems.

If you are bringing coax into the house then you want the house and tower grounded together. We do that here at our TV transmitter. Tower and all equipment racks grounded to one point. We regularly get struck by lightning, and in the two summers I have worked here, we have had only one lightning related failure consisting of blowing out 3 electrolytic filter capacitors in our aural exciter power supply, which appear to have been caused by a power surge on the AC mains.


  • Please forward any comments to me ( Rick) ve3cvg@rac.ca




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    This page was updated on August 3rd, 2001