Lightning protection cable impedence test

[waelatallah]

Hi,

I am working on a project where we have a lightning protection/ground system inside an urban building. The ground system is connected to the city's ground system and nearby buildings. The down conductors are all connected to re-bars in poured concrete foundation walls.

We need to install 3 inspection pits in a straight line at certain distances before the slab is poured.

I am not working on the lightning protection system and have no previous experience of it. But out of curiosity I would like to ask a couple of questions with people who are experienced with this type of system :

1- Someone was saying that the impedance test in 5-10-15 years is not important because the ground system is connected to the city's and that we would not be testing the impedance of the ground of the building itself. Is this a correct statement with the information I have given.

2- What does the impedance test actually tests? is it the ground resistance (gravel, humidity of soil, soil, etc...) in the building? I know that there will be 3 inspection pits. In the middle one they will intercept the conductor or rod. and in the other 2 they will install spikes in the ground and measure using ground-meter. How does this test work? I know one of the spikes will be for current the other one for voltage and V=IR. If the ground conductor is intercepted in the middle pit it will be connected to all the other ground conductors and I am not sure what we will be measuring?

I know this might sound vague because it is vague to me. If you need any other information in order to answer let me know.

Thanks.

 

[mgookin]

So you have an array or loop (braided cable?) at the top of the building with lightning spikes and that system is only connected to building steel without its own (braided) conductor going down to earth?

And can you describe the city's system? Never heard of a municipal lightning system.

 

[GoldDigger]

And can you describe the city's system? Never heard of a municipal lightning system.

Possibly just a reference to being connected to the service neutral, which will not be much use at all as a lightning ground, although the low frequency impedance might read fairly low.

For lightning protection a short, straight path with large diameter wire or wide braid is important. Much more easily evaluated visually than with any kind of meter.

The actual electrode to earth resistance is going to be of little or no importance, since lightning is extremely high voltage with high frequency components that care much more about inductance than DC resistance.