Tower grounding and lighting rod calculation?

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notmyspace

Member
Location
Maryland
Can anyone guide in calculating grounding for a 40 ft tower for camera? We will be installing a lighting rod and tie into the ground rod. Each leg of the tower will be CAD weld and tied into the ground rod. Wenner test is pending to get the soil resistivity.
Questions here are :

1) calculating the earth grid conductor sizing?
Should I use the equation 37 on IEEE 80 greenbook to calculate it?

2) How do you calculate number of ground rods required in order to get 5Ohms once we have the soil resistivity?

3) Do I need to calculate touch and step potential since there is no electrical generation beside the lighting rod?
 
T

thewire

Member
Location
Raleigh
electrofelon said:
Sorry to sort of dodge your question, but is someone saying you need all the grounding and that you need a certain grounding resistance? Step potential is an issue with high voltage systems.
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Hi there..no worry.

We are installing a 40ft tower for some CCTV. We have all the site plan completed. All the electrical piece for the equipment etc done. Structure analysis is completed. We need to put together a lighting rod and bond it to the ground ring. Also we need to cad weld each leg to the ring too. All will be connected to a ground bar for ease of connection.

Question, how can I determined number of rod need and using typical 10ft spacing and 10ft rod 5/8"? I am still waiting for soil resistivity to be tested. Also, for the conductor size, should I use that equation to determined the size or is that a faster way to do it, so when there is a fault, the cable won't melt if it take a hit from lighting.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Again, who is requiring the grounding? sounds like a lot of detail for a little toy tower . Is there an engineer or AHJ that is requiring the ground ring, cad welding, soil resistivity test etc? If I were doing this install and I wasnt installing to plans that spec-ed it, I would maybe install a ground rod and call it a day, although the rod is not even required by the NEC unless there is a feeder running to the tower which 'I doubt is the case. I believe that most people knowledgeable in grounding for lightning will tell you that the resistance to ground is not a significant factor in the lightning protection design. Yes this is contrary to what many engineers seem to think. I did several cell towers years ago and we were supposed to achieve 4 ohms. I have a 90 foot windmill tower and its not grounded at all and I have never had problems. I think much lightning protection is not based on science.
 
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notmyspace

Member
Location
Maryland
electrofelon said:
Again, who is requiring the grounding? sounds like a lot of detail for a little toy tower . Is there an engineer or AHJ that is requiring the ground ring, cad welding, soil resistivity test etc? If I were doing this install and I wasnt installing to plans that spec-ed it, I would maybe install a ground rod and call it a day, although the rod is not even required by the NEC unless there is a feeder running to the tower which 'I doubt is the case. I believe that most people knowledgeable in grounding for lightning will tell you that the resistance to ground is not a significant factor in the lightning protection design. Yes this is contrary to what many engineers seem to think. I did several cell towers years ago and we were supposed to achieve 4 ohms. I have a 90 foot windmill tower and its not grounded at all and I have never had problems. I think much lightning protection is not based on science.
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lol totally i forgotten i have registered before but it was from my home, no wonder

anyway, the client required us to installed grounding and lighting rod to protect the camera and also required to be 10 Ohms (checked their spec).
My understanding that lighting rod to the ground rod is determined how it was dissipate, and also depending what is the soil resistivity, the number of ground rods for 10 Ohms.
Based on ANSI T1.313, the conductor shall be #2 AWG bore solid copper conductor.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
First, a disclaimer: I do not consider myself very knowledgeable in lighting protection systems, but I will tell you a few things that I recall others on this forum saying over the years. Lightning dissipates into the ground very quickly and because of this, ground rods are not very effective. Better is to have numerous shallowly buried radials. Also as I mentioned before the actual ground resistance is not so consequential in dissipating a strike. Of course all this is moot if the person who writes the checks says "here is how I want it done, do it". I dont believe there is any way to tell how many ground rods you need to achieve a given value, or how many more you need to lower a value x amount. Do what we did on this one cell site and take your reading on a rainy day!
 
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notmyspace

Member
Location
Maryland
electrofelon said:
First, a disclaimer: I do not consider myself very knowledgeable in lighting protection systems, but I will tell you a few things that I recall others on this forum saying over the years. Lightning dissipates into the ground very quickly and because of this, ground rods are not very effective. Better is to have numerous shallowly buried radials. Also as I mentioned before the actual ground resistance is not so consequential in dissipating a strike. Of course all this is moot if the person who writes the checks says "here is how I want it done, do it". I dont believe there is any way to tell how many ground rods you need to achieve a given value, or how many more you need to lower a value x amount. Do what we did on this one cell site and take your reading on a rainy day!
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thank you sir. As for the number of rods and area for the ring, I found the method of calculating by

1) Calculate single grounding rod using nomograph and the resistivity from soil testing.
2) Using an estimated area in the proposed ring and rod layout per IEEE STD 142, each rod separation (optima is 2x rod length)
3) Using the Combined resistance graph, I will have effective resistance of the proposed layout.
4) Based on the graph, I will have my resistance ratio number and multiply with the results from #1, I should have my total effective resistance of the system.

Does it make sense?
 
Sahib

Sahib

Senior Member
Location
India
You need to see two things.
1) Any person approaching your tower during a thunderstorm is not endangered by lightning ground currents from your tower.
2)The equipment mounted on the tower or inside the cabin is not damaged by the lightning current flowing in your tower.
 
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notmyspace

Member
Location
Maryland
Sahib said:
You need to see two things.
1) Any person approaching your tower during a thunderstorm is not endangered by lightning ground currents from your tower.
2)The equipment mounted on the tower or inside the cabin is not damaged by the lightning current flowing in your tower.
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So, with a simple air terminal mounted on the top of the tower and grounded to the base ring with insulated copper wire. Each legs are grounded to the ring. The grounding system should have a 5 Ohms/10 Ohms Should that be sufficient?
 
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notmyspace

Member
Location
Maryland
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Haji

Banned
Location
India
notmyspace:
I think it is better to engage a lightning protection consultant for the objective one mentioned in post #8, for the link mentioned in post#10 does not describe it specifically.
 
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