Lightning Protection Ground reading

[KasseemF]

What is that standard for a good ground reading for a lightning protection system? Is it 25 ohms per rod and what should it be for the overall system?

I am getting a reading of 100 ohms on my system. What measures can be taken to rectify this?

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[petersonra]

What is that standard for a good ground reading for a lightning protection system? Is it 25 ohms per rod and what should it be for the overall system?

I am getting a reading of 100 ohms on my system. What measures can be taken to rectify this?

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One would think whoever designed the lightning protection system would be the correct person to ask such a question.

 

[Sea Nile]

Are you asking within the scope of NFPA 70? or is it an actual lightning protection system?

 

[tom baker]

A lightning protection system is a different standard from the NEC, and the NEC does not require 25 ohms. There are methods to reduce ground resistance, chemical rods, deeper rods, and those are beyond the scope of what we typically answer. As pointed out, ask the company who designed your system.

 

[Sea Nile]

A lightning protection system is a different standard from the NEC, and the NEC does not require 25 ohms. There are methods to reduce ground resistance, chemical rods, deeper rods, and those are beyond the scope of what we typically answer. As pointed out, ask the company who designed your system.

Thanks, I didn't want to assume. I admit I don't know much outside of NFPA 70, and only a little inside of NFPA 70.
The main reason I ask is I can't believe a lightning protection system would have a a ground resistance of 100 Ohms.

 

[tom baker]

Do you have resistance readings from when the system was first installed and periodic readings since then?

 

[don_resqcapt19]

4.13 Grounding Electrodes, in NFPA 780, Installation of Lighting Protection Systems, does not specify any minimum resistances or any resistance testing for a lighting protection grounding electrode systems.

 

[R777V]

Are copper plated better than stainless steel ground rods, or are stainless better under different circumstances


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[tom baker]

cu coated and ss rods are used for corrosion protection, not lowering resistance. Cu listed rods have a thicker cladding

 

[tom baker]

If you want to lower resistance, use sectional threaded rods and drive deeper.

 

[R777V]

All the stainless I have are sectional threaded, don’t think I’ve seen any stainless without threads, mine are from a hoard passed down from my old man who worked Substation Construction.


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[R777V]

4.13 Grounding Electrodes, in NFPA 780, Installation of Lighting Protection Systems, does not specify any minimum resistances or any resistance testing for a lighting protection grounding electrode systems.

Tom, how deep are we talking 20’? Or more, don’t want to strike oil or pound them to China either.


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[R777V]

cu coated and ss rods are used for corrosion protection, not lowering resistance. Cu listed rods have a thicker cladding

Tom, are we talking 20’ or sinking rods farther than that or a grid of 2 or more at 20’?


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[tom baker]

Tom, are we talking 20’ or sinking rods farther than that or a grid of 2 or more at 20’?


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Mike holt has a video showing testing resistance of ground rods driven to 50 ft. He was showing different ways of measuring GR resistance
The video may still be available at his website

 

[paulengr]

Lightning protection is based on SURGE impedance, NOT DC resistance. You are all way off base here. Ground rod testing is for system grounding. NFPA 780 gives inspection procedures (basically visual).

 

[tom baker]

I was answering about why cu clad and ss rods are used, and why drive rods deeper. How is surge impedance measured?

 

[don_resqcapt19]

It is interesting that NFPA 780 permits an 8' rod but requires the bottom end of the rod to be at 10' in the earth.

 

[tom baker]

Don we used to have a couple of members who were lightning protection system installers, useful on questions like this