Lightning conductors

[philip in china]

Does anybody know anything about the practicalities of making lightning conductors? We are erecting some here on the taller buildings.

So far we have forged points on some 5 foot lengths of 1/2" bar. These will be bolted onto the rooves and some 1" x 1/8" strip will be welded onto them to make the ground. This will be buried in the earth.

Is it really as simple as that?

[John B]

What material are you using? Normally I have used copper

[philip in china]

It will have to be in steel. I know copper conducts well but it will not be possible on this job.

[yesteryearforge]

Phillip
I think steel conducts better than trees and they dont seem to have any problems.
Dont know much about lightning except to stay out of its way but I think it really is as simple as that.

Mike

[MooseRidge]

Two of the biggest items to watch is the attachment point on the roof and the depth/location of the grounding strap....

If the rod is attched to the roof so that the anchors are close to any metal (flashing does not appear to have enough mass to matter) such as sprinkler systems, I-beams, cranes, etc. , lightning may ignor the grounding strap and arc to this metal.

Same situation with the grounding rod. Watch out for buried electrical lines and water mains as the lightning with jump to them. Usually, the strap is attached to a 6' rod hammered into the ground with only 2" or 3" showing....

[steve sells]

I am a Master Electrician with IBEW Local Union Number 305. Code is clear about this, but since you are not in the states. it is up to local authorities.

What is important is good path to earth for a lightning strike to drain off, Remember Its a very high power electrical charge, no matter what you use, when it gets hit it can become toast. But its lazy. Electricity will travel the easiest route. so if your Rod is a better path (less resistance) than the surrounding area, then it will follow that path. Your conductors likewise should be an easy path, large enough to deal with a high power transfer, at least a diameter as your finger as smaller wont last, this usually means Copper wire. as Gold is too costly, and Silver is not much better.

Steel is used for most grounding rods, they are only copper coated. the rods for lightning as well. Use 1/4 inch strapping 1/2 inch or wider should be a good connection point to the rod, larger is fine, but 1/8 is too thin to hold up to a strike.

For the record, when I mention lasting, it is not about years, its about lasting long enough to drain the lightning strike. its not any good if it melts at the first hit, before it can drain the electricity.

[markb]

Another Master here Lu #595. I worked on a building at a military base and we had to install lightning rods. We used multiple rods all connected together with multiple leaders down to many rods. As Steve said path of least resistance, make it easy to get to ground.

The bible of design is NFPA (national Fire Protection Agency) publication 780, tells you everything you would ever want to know.
Here's some interesting reading.
The Straight Dope: Do lightning rods really work?