150 foot Rohn Tower grounding

[copper123]

The other day I wired up two small shelters that sit at the base of two 150 foot rohn towers. 1 guy wires at each corner. This is a private installation. The two towers use line of sight to communicate with each other. They are about 30 miles apart. Forgive my ignorance, but they are for communication at that is about all I know. My scope of work was for a electric heaters and one 20 amp, 120 volt equipment outlet at each shelter. Anyhow, the owner had not done any grounding what so ever to the towers to date. I asked him if he was going to install a counterpoise or what the manufacture suggested to do proper grounding and bonding. His reply was that he had not addressed it yet! I have been digging around in the code and come up with Article 820, but not a lot of information. Does anybody have any direction on this? I am not doing any of the work, but I would like to learn as much as I can. Also, the electrical service was a 3 wire. It was a conduit coming up to the shelter, 60 amp rated non fused disconnect, Green bonding screw in place (Main bonding Jumper). No ground rods in place at the time. Thanks for any words of wisdom. This kind of work is completely new to me, and I have never dealt with it before. Its would seem that the tower industry would be pretty specialized.

[ November 07, 2005, 11:40 AM: Message edited by: copper123 ]

 

[bphgravity]

Re: 150 foot Rohn Tower grounding

Perform a search on "tower grounding" under the Grounding verses Bonding Forum. You can read there lots of fact and opinion on proper communication tower grounding systems.

 

[copper123]

Re: 150 foot Rohn Tower grounding

Thanks, I never even thought about doing that! I will start my search now.

 

[tom baker]

Re: 150 foot Rohn Tower grounding

The towers fall under Art 810.
Coax is under Art 820
Each tower needs a connection to a grounding electrode system, then this system is connected at one point to the building electrical grouding system.
I use a 8 ft copper clad rod at the base of my antenna masts, then bond to the building electrical ground, I use 2 AWG as the cost is not that much over the 30 year life of the installation.
The coax will typically hit a impulse supressor right at the entrance to the building, this impulse supressor is bonded to the tower ground system.
A good resource is a book by Polyphase called the grounds for lightning and emf protection.
Also check the polyphase web site for white
papers.
The antenna coax shield may need additional grounding if its more than 100 ft long.

 

[copper123]

Re: 150 foot Rohn Tower grounding

Thanks Tom I sure appreciate the information. I am starting to study/learn/understand the world of tower grounding now. I might have a few questions however.