lightneing arrestors 1

[chiplonkar]

On high rise buildings and towers, we put lightning arrestors. Can any one give me the guide lines with figures and formulas, on number of arrestors to be put in existing factory premises ? Are there rules which specify how much area one arrestor will cover ? Are there guide lines for earth resistance for such arrestors ?

 

[jbartos]

Suggestion: It is more appropriate to refer to lightning rods or air terminals.
One good source is NFPA 780
Visit

http://www.nfpa.org

for more info.
This approach is based on Faraday Cage principle.
Usually, it is applied to a large footprint low height structure.
Early Streamer Emission principle is based on
Franklin Cone principle
Usually, it is applied to a small footprint high structure.
Visit

http://hearybros.com/english/index2.html

etc. for more info

 

[AusPowEng]

If you are not in North America, you may find the IEC standad would be applicable in your region. The document is IEC 61024 (series) 'Protection of Structures against lightning'. There are a couple of parts to this standard that collectively covers the risk assesment of structures. to the selection and placement of air-terminations.

As far the resistance to ground goes, 10 Ohms is the target resistance of the lightning earthing system.

The most effective stake design that I have seen is a shallow rod electrode (3m) with short (400mm) horizontal feeders radiating from the bottom (like an inverted propeller).

 

[busbar]

chiplonkar, you refer to “lightning arrestors” but do you mean “air terminals”?

 

[Kiribanda]

Hi chiplonkar,

Your requirement merely depends on the fact that how much your building is exposed to direct lightning strikes. In other words before you invest on a typical ligtning proetction system you have to do a risk analysis. For that you need to follow the methodology specified in detail in BS 6651 ( IEC 61024 does not specify any methodology )and conclude how much is your risk factor. Then you can specify how many air terminations and down comers you need.Also it specifies how much resistance you have to have for an individual electrode and when all the electrodes are connected as grid etc.

In addition you have to consider other design aspects with regard to indirect lightning strikes such as coupling etc.

NFPA 780 too covers the subject very widely which is used in ANSI world. But I personally feel BS 6651 is better which is widely used in the IEC world.

Regards!

Kiribanda