Steel Roof Grounding

[Powereng]

I'm not a lightning expert by any means, but in the electric utility field we run a single #6 copper ground wire from the bottom of the lightning arrester, down the pole, to a ground rod at 25 ohms or less of resistance. This is considered sufficient enough to dissipate the electrical energy of a lightning strike enough to protect our equipment on the pole. Now I've seen hundreds of MOV arresters blown to bits because they failed, but never a burnt ground wire running down the pole.

 

[Zerk]

Well, I mean if the grounding system is still in place. The rods would only be inches above the steel roof. And besides, I have a steel plate over my chimney flues. That is higher and is grounded.

I designed one system in 98, so no expert. The light rods should be higher then anything else, I don't remember exceptions. The height is dicated by how many you put up, higher, you need less. They are ran to ground.

I have no experience or calculations, but if your system is designed right and grounded, I doubt grounding the roof would help.

The problem with grounding the roof, is each sheet is not bonded to the next. You would have to ground each piece, to meet met NEC code for electrical bonding in general. Lighting is protected by fire code. Not sure what they say about metal roofs. It could be googled.

With big electrical faults I tend to think it will burn through the paint. Maybe not on household faults. But I the airels are supposed to be first contact.

 

[CalG]

Now I've seen hundreds of MOV arresters blown to bits because they failed, but never a burnt ground wire running down the pole.

That's because you have not seen a direct hit on the pole. the pole will show the damage. if it is still standing.

 

[Zerk]

I'm not a lightning expert by any means, but in the electric utility field we run a single #6 copper ground wire from the bottom of the lightning arrester, down the pole, to a ground rod at 25 ohms or less of resistance. This is considered sufficient enough to dissipate the electrical energy of a lightning strike enough to protect our equipment on the pole. Now I've seen hundreds of MOV arresters blown to bits because they failed, but never a burnt ground wire running down the pole.

I think we use 4/0, atleast in the station.

The arrestors become the path to ground. The resitance is high enough that current will not flow for normal voltages. If they blew, it may be failures, or it may be a close hit. I don't know.

 

[Powereng]

Yup, subs are a different beast altogether. Lots of 4/0 copper wire bonding everything together, with a complete ground grid underneath. The name of game is to dissipate as much of the lightning strikes electric energy into the ground as possible. The reason we only use #6 on the poles is probably because the **** copper thieves come along and cut all my ground wires off the poles and sell it for scrap.

 

[Industrial Toys]

I am no expert either and not in that field, but I agree, I have never seen or heard of a grounding conductor for the purposes of lightning being burned through. If this were the case, I'm guessing they would have had to re-think their conductor size calculations a long time ago.

My chimney plate is maybe six feet long and maybe three feet above the roof peak of a forty or so foot long roof. Are the two other foot long lightning rods on the peak doing anythng at all for protection?

 

[Zerk]

My chimney plate is maybe six feet long and maybe three feet above the roof peak of a forty or so foot long roof. Are the two other foot long lightning rods on the peak doing anythng at all for protection?

There not hurting. But the idea is to be above everything. I don't know much about it though. Years ago, I used NFPA to figure out how many and how high for an apartment roof. Flat roof.

I'd talk to a company that sells them.

 

[Powereng]

There not hurting. But the idea is to be above everything. I don't know much about it though. Years ago, I used NFPA to figure out how many and how high for an apartment roof. Flat roof.

I'd talk to a company that sells them.

Company I've worked with in the past when dealing with customer lightning issues. intropiece

 

[CalG]

Check these pics

Would a 4/0 wire have made a difference?

and yet most "lightening rod" installations are smaller gauge.

lightning strike damage - Google Search

 

[Zerk]

4/0 is expensive.