# Grounding 90 foot radio tower



## Victory Pete (Jun 29, 2012)

I had a service call to a small radio shack for a local fire station repeater. Lightning has damaged some radio gear and outlets. The original grounding was very poor and obviously inadequate. How should this be corrected? I am thinking of adding new 3/4" 10' rods and new copper ground wires. I used to do a lot of grounding for cell sites in the 1990's. We used tinned #2 solid copper, 3/4" 10' rods and it was all CadWelded.


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## HARRY304E (Sep 15, 2010)

Victory Pete said:


> I had a service call to a small radio shack for a local fire station repeater. Lightning has damaged some radio gear and outlets. The original grounding was very poor and obviously inadequate. How should this be corrected? I am thinking of adding new 3/4" 10' rods and new copper ground wires. I used to do a lot of grounding for cell sites in the 1990's. We used tinned #2 solid copper, 3/4" 10' rods and it was all CadWelded.


I think that article 820 covers that.


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## drsparky (Nov 13, 2008)

The grounding of a site is much more than a few ground rods. _Motorola R56_ is the standard for the industry.
http://www.radioandtrunking.com/downloads/motorola/R56_2005_manual.pdf


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## Bbsound (Dec 16, 2011)

I am just talkin'
But it seems like a metal tower in a huge concrete base in the earth would be a pretty decent ground.


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## Jlarson (Jun 28, 2009)

What Drsparky said. 

You can always sub to a wireless service contractor if you are unsure about applying R56.


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## 8V71 (Dec 23, 2011)

Bbsound said:


> I am just talkin'
> But it seems like a metal tower in a huge concrete base in the earth would be a pretty decent ground.


I did this job a long time ago, and technology may have changed, but at the time Rohn wanted lightning strike energy to find another path besides the concrete base if possible. It could have been a CYA thing, I don't know. They didn't want the tower support J-bolts touching any of the rebar and the legs were bonded to ground rods.


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## Jlarson (Jun 28, 2009)

Just the concrete base is ok for a site light pole but radio gear a different ball game.


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## Speedskater (Oct 2, 2009)

Pages and pages of small tower grounding:

http://www.w8ji.com/station_ground.htm


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## RIVETER (Sep 26, 2009)

8V71 said:


> I did this job a long time ago, and technology may have changed, but at the time Rohn wanted lightning strike energy to find another path besides the concrete base if possible. It could have been a CYA thing, I don't know. They didn't want the tower support J-bolts touching any of the rebar and the legs were bonded to ground rods.
> 
> View attachment 28865
> 
> ...


This is just my thoughts but even if the j-hooks were not touching the re bar the concrete between would be a good enough conductor to allow, at least, a partial lightning current to flow anywhere in the concrete, and the resultant resistance OF the CRETE causes the current to heat the moisture and then blow the CRETE. Any diversion of ANY aberrant current should be started above ground....IMO.


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## chewy (May 9, 2010)

The cell tower I worked on had a 150mm wide 5mm thick copper strip buried around it 800mm deep.


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## ceb58 (Feb 14, 2009)

Bbsound said:


> I am just talkin'
> But it seems like a metal tower in a huge concrete base in the earth would be a pretty decent ground.


We have some towers that have taken direct hits and it has blown chunks out of the base's. Then we have to bring in engineers to check the piers. 



chewy said:


> The cell tower I worked on had a 150mm wide 5mm thick copper strip buried around it 800mm deep.


We use #2 tin coated solid welded to the rods, tower legs, fence post and then the most important part it is brought back and tied to the utility grounding.


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## don_resqcapt19 (Jul 18, 2010)

ceb58 said:


> We have some towers that have taken direct hits and it has blown chunks out of the base's. Then we have to bring in engineers to check the piers.
> ....


Were the rebar and anchor bolts bonded to the grounding system?

I read about a power company having this issue and they found that if they made sure everything in the concrete was bonded together, that they did not have that problem. The standard rebar tie wire was not enough to prevent the problem.


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## ceb58 (Feb 14, 2009)

don_resqcapt19 said:


> Were the rebar and anchor bolts bonded to the grounding system?
> 
> I read about a power company having this issue and they found that if they made sure everything in the concrete was bonded together, that they did not have that problem. The standard rebar tie wire was not enough to prevent the problem.


Each tower leg has a jumper cad welded to them and to a g rod with the ground ring. So the bolts would be grounded through the base plates but the rebar is just tied. There is not a direct connection to the grounding system.


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