Down conductor for Lightning arrestors

Since all of you questions deal with electricity and the NEC why don't you just buy a copy of the book?????????????????
National Electrical Code

If you're not familiar with lightning, you might want to have someone else do this and watch them a few times. There are pitfalls such as bends and adjacent metal that you might never think about until you have 20,000 A rising in 10 microsec.

Having been physically hit by lightning twice in my life, which i can assure you with the utmost confidence it is NOT nearly as funny as in the cartoons, TVP45 is absolutely right!! If this is not your field of expertise go and find somene who is.

while electricity is in general a cruel and unforgiving bitch, with the proper controls and precautions she can be reasoned with. Lightning however is her psychotic and out of control sister who drinks WAYYY to much coffee....

The roof of our station was just repaired. The original rods were connected with bare braided copper wire. It was unlike anything that I have ever seen in automotive or other electrical use. The newly repaired roof also used new copper of the same design, but also added some similar wire to connect roof mounted air conditioner components, BUT this wire was aluminum.

I would also like to know what the rules are.

The braided cable you saw was flat, right? That is usually the case because flat braided cable will carry more high frequency current than round.Under high voltage and high current, electrons repel each other and travel mainly on the surface of conductors, therefor the advantages of the flat braided design.

Separate ground rods are not approved by the NEC unless they are bonded to the main power ground rod.Multiple ground points create current lops that can generate high voltages.Consider 100,000 amps going thru .1 ohm of resistance.The voltage generated is 10000 volts.

Aluminum is normally chosen for lighting grounding because for the same cost, a larger conductor can be had, and the physical strength increases with size.Remember, the surge is for a very brief time period.The aluminum for lightning rods is usually a spirally twisted square or Tee shaped conductor that gives more surface area for the electrons, and the ability to self-support around building finished surfaces, etc.

Reference the NEC article 250 for more info on bonding and grounding.

Braided is not exactly correct. The wire is round, about .450 diam. It is composed of six groups of four strands twisted around each other. The size of each wire in the strand is .030 to .035. I understand that current travels on the surface of a wire, but why are the strands so thick for lightning protection? The wire has a label for UL compliance for lightning protection.

The size is large to afford physical strength for the conductor.It can be formed into a smooth loop or "ell" around obstacles without using insulators or stand off brackets.Lightning does not like sharp turns and will jump off of the conductor if any sharp bends are made.The large individual size also prevents fraying of the surface, which could create a corona effect.Imagine fine wires with split ends, forming many emitter points.Not good.

Construction of this main conductor varies in shape and form, but has the same purpose.

The flat braided wire I spoke of is generally used on roof top machinery to isolate vibration from the main conductors.

Hope this helps,but still you need to do further study before taking on a job solo.

Forgot to mention:The large physical size and high tensile strength also prevents"whipping" of the conductor when carrying high currents.Imagine a party favor that you blow on that uncurls under pressure.Similar effect with high current.

Thanks.

but still you need to do further study before taking on a job solo

Not a chance I would take on a job like that! But, what is your opinion of a pair of rods, self installed on my house?

If you pack the chute, you are welcome to jump with it.