Metal Roofs & Lightning

[Pettrix]

Is it OK to run a ground strap from a metal roof, down to a ground stake buried deep under ground to help disperse a lightning strike on the metal roof? Of course I would be using heavy gauge wire to handle the voltage.

Monsoon season will be here in a month or so and I figure if a lightning strike hits my metal roof. It's best to take that charge and disperse it into the ground to prevent damage.

 

[CobyRupert]

Metal Roofs & Lightning

Yes.
A ground rod is ok. Multiple connected rods are better. A bare copper wire loop is better. Underground water pipes are better. More surface area in contact with earth is better.

More down straps than one to underground electrodes are better.

In U.S., a document called NFPA-780 recommends installation methods.

 

[Tractor Seabee]

Re: Metal Roofs & Lightning

Yes.
A ground rod is ok. Multiple connected rods are better. A bare copper wire loop is better. Underground water pipes are better. More surface area in contact with earth is better.

More down straps than one to underground electrodes are better.

In U.S., a document called NFPA-780 recommends installation methods.

If I remember 780 has a map showing probability of hits by zone. Max protection is provided by lightning rods tied to a grounding system. That system is attached to the roof and the frame also. New buildings they use the rebar system in the foundation as the grounding electrode. The NEC also address lightning protection. NFPA 780 is fairly expensive. I use SOARES Book of Grounding and Bonding (available on Amazon) for both electrical system and lightning protection. It references both and brings it into understandable terms. Grounding and bonding is the most mis-understood subject in the electrical world. I spent quite a few years doing Construction Quality Control and inspected these systems for compliance with NFPA 70 (NEC) and 780. Carried both in the truck along with Soares. Learned a lot in those years.

Ron

 

[Pettrix]

So would I have to install Air Terminals (lightning rods) on my metal roof or can I supply just install a clamp on the standing seam part and then run a cable from that clamp to an underground rod?

If lightning hits the metal roof, the roof panels are all connected with metal to metal connections. I was told Air Terminals are only necessary for NON-metal roofs since the lead from the strike needs to contact a metal terminal to prevent hitting a NON-metal roof.

Any good place online to order the supplies?

I was looking at LightningRod.com

 

[Roadworthy]

You might want to do some reading before you go shopping. Lightning tends to strike higher points, be it a tree or a building as opposed to the general terrain. It will seek a point rather than a flat surface. Your Air Terminals will provide such a point and should extend somewhat above the roof itself. They are usually electrically isolated from what they're protecting. You need to determine if your goal is to use the roof as a lightning rod or use rods to prevent lightning strikes to your roof.

 

[Pettrix]

You might want to do some reading before you go shopping. Lightning tends to strike higher points, be it a tree or a building as opposed to the general terrain. It will seek a point rather than a flat surface. Your Air Terminals will provide such a point and should extend somewhat above the roof itself. They are usually electrically isolated from what they're protecting. You need to determine if your goal is to use the roof as a lightning rod or use rods to prevent lightning strikes to your roof.

The Air Terminals are aluminum and they attach directly to an aluminum roof. There is no insulation or isolation between the Air Terminal and the metal roof. It's metal on metal contact. Plus the aluminum grounding cable sits directly on the aluminum roof from the Air Terminal.

On non-metal roofs, the Air Terminals are mandatory because wood, asphalt, shingles, etc. cannot transmit electricity. So there needs to be a metallic point of contact for the lightning lead.

 

[Industrial Toys]

I wondered about this for years. None of my outbuilding metal roofs are grounded. I did replace my house roof with metal and it is grounded via the existing lightning rods, but how much electrical integrity is there to painted steel connections?

I always worried on the barn of the lightning hitting the roof and flashing over to electrical services, not designed to carry that current. It hasn't happened in many decades though.

 

[Tractor Seabee]

Pettrix, out there in Mohave desert what is the risk to start with? I grew up in the desert of AZ and nobody worried because lightning strikes were not that common. Taking risk is what insurance is for. Just don't work out there during a lightning storm. Low risk means low cost prevention. Several points from other posts: Strikes at the high point like a ridge is true; Aluminum as it ages gets corrosion on the surface which increases the resistance which slows down transmission of current and builds heat; I have never heard of aluminum terminals, worked some around power lines and those were always copper; everything metal in the building needs to be bonded together, including water and gas piping; NEC requires the electrical service grounding system and the lightning system grounding to be bonded together; copper is a better conductor of electricity than most other common metals except gold and silver.

I can envision a poorly grounded aluminum roof 10 years old with steel or SS fasteners (asking for corrosion) getting a big molten area with direct strike.

Think Risk, Ron

 

[breadtrk]

There is some partly good advice here.... first wire won't do squat, needs to be copper strap, fat copper strap. even then, it don't matter how much copper you have invested it IF you get a direct hit. You can use 6" strap from every roof panel straight to 20 ft rods in a swamp, it won't matter. As others have mentioned, insure it and let your storm god determine what happens.