Friday, July 29, 2011

Grounding System Construction

I wanted to take a few minutes to document the construction of the grounding system for my station which I did a few years ago.   This is an often confusing item for newer hams and maybe this will give some ideas that can be used or expanded on by someone else.

The basic design consists of a weather sealed single point box, that all the EMP/lightning arrestors are installed into, and all the antennas come in through that box connected to an arrestor. That box has a ground connection that goes into the shack for a single ground bus inside for connecting the antenna switches and for other inside grounding connections.

I used an aluminum NEMA style weather proof box I was able to find cheap as surplus, to mount all my arrestors. A single ICE HF arrestor is shown in the photo, there is a second ICE Arrestor for VHF, and a Polyphaser HF arrestor mounted in there today. You can see the 2" copper strap was attached directly to the aluminum panel inside the box, and the arrestors are screwed into the box on top of the copper. The copper is polished first using a scotchbrite, and then the arrestors are mounted using coatings of Anti-Oxidant such as that available from IDEAL Industries. This will help ensure a long life electrical connection between the parts.

For the COAX, holes were drilled into the sides, and weatherproof coax connectors were used to seal the coax passthroughs. They worked very well, and are available from DX engineering.

The box is mounted on a PVC pipe put into the soil under the window that leads to the shack which suspends it a few feet off the ground. A ground rod is in the ground just in front and under the single point ground box. The copper strap from the single point box connects to the ground rod underneath it, and an additional copper strap goes through the window into the shack to connect to a grounding bus on the inside.

On the inside, the copper strap passing through the window is mounted to a board that has another copper strap attached to create a grounding bus for things like antenna switches, tuners etc. This photo shows the board sitting on a small desk, but now This board is now mounted to the wall directly under the window with more switches added to it. (You can see a peek of it in one of the photos of the FT-450 Jack Repair Page).

From the main ground rod just below the single point ground NEMA box, there is grounding strap run underground to several other ground rods in a radial pattern at more than 8 feet apart in every direction.

For the other ground rods, a string was pulled to them to make a straight guide line, and then a trench was made for the copper strap a by just wiggling a hand spade/shovel to allow for putting the strap a few inches under the ground.

This was repeated to several more ground rods.

For each one I used a mechanical connection between the copper straps and the ground rods. A good physical clamping connection is the easiest and pretty reliable using the sort of clamps I used which are made for clamping strap, and again the process of polishing all the copper surfaces and coating them with anti-ox before making the mechanical connections was used.

This photo shows the flat clamps used for the strap, and a single wire clamp used for a the #4 wire that was connected to the interior electrical breaker panel.

Since I didn't have enough of the custom strap clamps for all the ground rods, on one of the strap-to-rod connections I used another connection method that someone suggested. It involves forming a tube on the end of the strap and placing over the top of the rod, and then mechanically clamping it into place. This method actually worked pretty well, so if you don't want to spend the money on the strap clamp which are a little expensive, I think that it might be a good way to connect your system. Again, use the same process of polishing all copper surfaces to remove oxidation, and coat with anti-ox compounds before clamping together.

At the ground rod closest to the side towards where the electrical panel is located, a #4 gauge wire was run from the ground rod to the ground bus in the interior electrical breaker panel. This ensures that all ground connections are bonded together and at equal potential. This is an often overlooked step, and is in fact required by national electrical codes(NEC).

When all was completed, I ended up with a fairly decent grounding system for a home radio station, consisting of 5 ground rods all connected to a single point grounding entrance panel.

Here is a layout of the final system after it was completed.


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