I recently received an email about the proper method to ground a home and the equipment in it as well as an 11 meter tower for antennas. The email came from Tomy in Croatia, it’s nice to know The OnLine Engineer is being read over there.
Tomy’s question is basically this – How do you properly ground your radio equipment contained in your house when it’s connected through coaxial cables to antennas mounted on a metal tower. Should you ground everything to the tower’s ground or only to the house ground? So the basic question is what is the proper way to ground a setup like this.
As a disclaimer, I am not an electrical engineer nor an expert on lightning protection, so if you follow any of all of these suggestions you do so at your own risk. I can not and do not guarantee that your equipment or your self will not be harmed during a lightning strike because you followed what I have written below. Now thats out of the way, here we go.
Here’s your answer Tomy, and if anyone has something to add please let me know by adding your comment below.
Every house’s electrical entry point is bonded to an earth ground right there. The neutral is connected to a cold water pipe or to a grounding stake that’s driven into the ground. This should be the only earth ground for the home’s electrical system. After this point the neutral and ground wires perform separate functions. The neutral is the return path for the electrical circuit made by plugging in an electrical device. Due to the large amount of current the neutral may be carrying a voltage difference can develop between the neutral and the ground wires, this is caused by the electrical resistance of the wire carrying the neutral current, this is normal.
The ground or Safety Ground’s sole purpose is to drain away any stray current from the Hot wire of even the neutral if it comes in contact with the ground circuit. If a piece of equipment has a metal case or frame it is attached to the Safety Ground. If a wire within that carries any electricity comes in contact with the case or frame the current will be drained off to the earth ground at the other end of the ground wire where the power came into the house. Normally no current is flowing in the Safety Ground so the voltage is at zero at all places within the wiring system.
When I moved my electrical service (circuit breakers and meter) at my house I had to drive a 10 foot (3.5 meter) grounding rod into the ground right next to it. This is where the neutral and ground meet in my house. And when the cable TV provider brought their coax cable into my house they placed an F connector Grounding Block to it just before it entered my house, they attached a heavy ground wire to the block at one end and the other to this same grounding rod. If the coax cable became energized, instead of the electrical current flowing into my house and to my cable boxes the Grounding Block would drain off any energy to ground before it could damage my home or equipment. (Heres a little story about just that.)
Cold water pipes have been used for many years to get good grounds within a house but today many homes are built with plastic pipe, which does not conduct. Also some people would mistakenly use the hot water pipe to attach grounds to, as the hot water pipes must pass through a water heater they loose their conduction path to earth ground. For this and other reasons all new or upgraded installations require the hot and cold water pipes to be electrically bonded at the water heater.
Tower Grounding is not my area of expertise and I refer you to the ARRL (American Radio Relay League) has many great articles on grounding in general and towers in particular and you can find them here - ARRL Lightning Protection.
Basically a tower should be grounded using a radial system, where heavy cables or copper straps are bonded to the tower and they radiate out away from the tower in several directions. Along the path of each of these radial grounding rods are driven into the ground and bonded to the radial. If lightning strikes the tower a properly designed and installed ground system will drain away most of the lightning’s energy into the surrounding ground.
To prevent the excessive energy from finding it’s way into your equipment via the coaxial cables lightning protectors are used on all lines coming from the tower. These should be mounted just inside the building and all of them should share a common single point ground. That may be a copper plate that all lightning protectors are mounted on, the point is to not have the lightning protector’s grounds at different potentials, which won’t happen if they are all attached to the same copper plate. They also have lightning protectors for telephone lines as well as electrical lines. PolyPhaser is a very good source for this type of protection.
They also want you to add a grounding wire all the way around your house and to bond this to your electrical service ground and the tower radial ground and this in turn to the copper plate where all the lightning protection is mounted. To do this right requires a lot of work. You should read the ARRL articles mentioned above.
Here is another link to more information on Lightning protection http://www.astrosurf.com/luxorion/qsl-lightning-protection.htm
I hope this helps, Russ