Grounding

This discussion is in relation to lightning protection for person and equipment protection.  It is a huge subject and everyone seems to have their twist on it.  You will hear everything from "why ground things, it attracts lightning?" to "I'm safe, I disconnect my equipment when there are storms near by."  That is all pure unadulterated RUBBISH!  Properly bonding and grounding equipment is the only answer.  My equipment has probably taken a dozen lightning hits and the only damage I've had was to a telephone (that I subsequently added a PolyPhaser phone line protector) and to a couple of computer modems (I then started using the protection supplied in the UPS systems).  But, don't  take my word for it.  Check with commercial and broadcast engineers.  Check the material Motorola provides.

The most graphic way to think about this issue is to picture the largest ground foot print you can create with the least reactance possible to that path.  Immediately you should recognize the power ground system and other utilities.  It's not being cheap that the phone and cable TV companies want their ground connections bonded to the power ground.  It does two things.  It provides a large low resistance path to ground and of great importance, it puts all of the respective grounds at the same potential when there is a voltage/current surge.  It follows that your Satellite receiver and ham gear should treated in the same manner.

In general, all of your antenna leads will conveniently enter the house in one location.  That is where individual lightning protector should be placed on each line.  Those devices should be connected together and a large ground wire run to the power ground.  A friend removed a basement window pane and replaced it with a copper plate.  He uses bulkhead mounted protectors.  In his case, the power entrance is just a few feet away.  The result is a very efficient and clean installation.  It doesn't hurt to put a ground rod at this point, but in fact, it may be redundant to the power ground.  The figures I've heard say that multiple ground rods must be at least six feet apart to have any additional effect.  Indeed, the power company requires two ground rods driven six or more feet apart when you have service installed. 

However, it's not quite that simple.  Personal and equipment safety boils down to NOT creating opportunities for large potential differences to happen at any location that people or equipment can be affected.  One must also consider other possible other conductive building materials such as water pipes, gas pipes and heating ductwork that may be at ground potential, but not referenced to antenna or power ground.    My home is built in an L shape so all of the utility pipes happen to pass by the antenna line entrance to the house.  A single run of #4 copper wire  and a bunch of ground clamps picked them all up in one short length.

I mentioned the value of creating as large a footprint as possible.  At the tower base there should be two, three of four ground rods driven 6 to 10 feet out from the tower and connected to the tower with #4 copper wire.  And, a #4 or better wire should be buried from the tower along with the feed lines and control cables to the building entry and connected to the common ground.  Preferably the wire should be uninsulated and laying in the soil, not in a conduit.  If possible, one would ideally locate a tower away from their house  to avoid droppings from birds and ice on the roof and possibly to avoid people climbing it to gain access into the house (although, it does make a handy ladder to get on the roof).  In this case, the ground footprint is enlarged providing more area for the lightning to disperse.

   

Here is a drawing of a typical grounding system.

 

I've seen several thousand dollars of equipment damage done where the operator had disconnected his antenna leads.  The lightning came into the shack via the transmission lines and wanted to go somewhere.  A few feet to the nearest radio and equipment it was connected to was the best path and it did it with ease.  The other problem with relying on disconnecting antenna leads is sooner or later you won't remember to disconnect the leads until you hear thunder.  That's exactly what happened to a friend of mine.  He claims when he went to disconnect the line he ended up sitting across the room on the floor.  Worse yet, there can be large static discharges ahead of storms or even independent of storm activity.  You never know when it may happen. 

You can easily estimate the costs of your equipment and insure it for replacement value.  You can't estimate the value of your life or a family member or even the value of the inconvenience of the paper work and getting everything replaced.  Insurance isn't the answer.  To put it bluntly, that's just a way of getting others to pay for your lack of concern or ignorance.  It's best to just do it right.

EST 31/07/2007