Grounding a Tin Roof

[Slamfire]

There were rods on my Granddad's barn that didn't have any connection to the ground. That barn has weathered 5 generations worth of storms with nary a problem. However at least two houses have burned due to lightning strikes nearby.
The lightning may not bother the house, but it looks as if teen aged boys are gonna strike that yard pretty soon. /forums/images/graemlins/grin.gif

 

[dmccarty]

Just saw this in the morning paper regarding lightning protection. It is interesting that the NFPA has standards on this issue.

http://www.newsobserver.com/news/nc/wake/cary/story/1275623p-7397317c.html

NFPA has a book, http://www.nfpa.org/catalog/product.asp?pid=78000&query=lightning&link%5Ftype=search&src=nfpa on the subject, it is $32.25 and it is NFPA 780.

I just found this reference for boats. Its very interesting.
http://www.cdc.gov/nasd/docs/d000001-d000100/d000007/d000007.html

Same site as the last one but for the "farm."
http://www.cdc.gov/nasd/docs/d001001-d001100/d001010/d001010.html

Anyone have access to this book and can give some insight?

The first article mentions spending $80 to protect a house.

Later,
Dan

 

[Inspector507]

I can access NFPA780 online, but I have a meeting this morning. I will try to look at it later today.

 

[rwinter]

Any idea what the cost is to have a professional install 5 or 6 lighning rods?

 

[tommu56]

rwinter

You might want to start a new thread too this one is over 5 years old till your post.

I'm an electrician and don't see why you would want any thing to draw lightning to your building this is only my opinion of lightning rods.


tom

 

[eepete]

My tin roof is grounded. I have tin gutters and downspouts. There is a stainless steel strap from the roof to the gutter, and then at the ground I use another strap held by a hose clamp to go "tin" (really zinc and tin) to stainless, and then stainless to copper for the ground run.

When building the house, I put in lots of copper around the house at foundation level and about 600' in four trenches that had other stuff at the 2.5 foot level, so that's my grounding system.

I claim that your metal roof and the earth all look like ground to any pending strike, so that grounding it doesn't really change the odds you'll be struck. What it does do is give a path for the charge to go to ground. Don't know if this is better than a "real" system with sharp pointed things in the air, but it has to be better than nothing. I've seen lots of houses that have been struck by lightning with results for nothing to burned down. This was an easy thing to do that substantially increases my ability to survive a lightning strike.

Driving in ground rods is not difficult, it's just hard work. You can get the rods and the #6 wire from big box stores. The biggest thing to avoid is a direct copper to tin connection. The tin will corrode. I also go around the house and hit the" tin 2 stainless 2 copper" areas with some WD-40 about twice a year to keep the water out and to inspect for any problems.

 

[/pine]

In older residences that have cast iron plumbing (waste) lines where the vent stacks penetratin the roof pose the biggest attraction for lightning strikes because they offer a solid ground...

I would think that a metal (cunductive) roof would dissipate the the energy of a lightning stirke similar to the way it is dissipated when a sailing vessel is struck...I would guess that grounding does very little to protect against a strike...

 

[eepete]

/pine is right. The concept of "protecting against being struck" can only exist in the mind of a salesperson. All of this is about dissipating the energy _when_ you get struck.

And speaking of sailing, when you've got that trench open or ground rod pounded in, add a sacrificial anode (hunk of zinc) in there for good measure. You can get that at a boat shop.

Pete

 

[n8wrl]

As a ham I've spent quite a bit of time researching lightning protection for my two 72' towers. There is no such thing as preventing a strike - spikes and other widgets to 'dissipate static in the air before a strike can happen' are useless. As others have said it's all about routing the _bulk_ of the lightning where you want it to go.

I say 'bulk' because lightning is electricity and if multiple paths to ground are available it will take ALL of them - just in varying degrees of current depending on how good of a conductor it is. It sees the path to ground as a bunch of parallel paths - it takes them all! Even if you have the fattest of cables to ground you will still get a tickle on smaller cables (satellite feeds, outside antennas, etc.) because they present yet another path to ground - thru your house and equipment.

Lightning is also an AC waveform which means it is very much like radio. And it prefers to travel on the 'skin' of a conductor - believe it or not a wide strap is better than a big fat cable - more surface area. Also, the route to ground should not have sharp bends or curves. These present an 'impedence bump' to lightning and not as much of the energy will take that path - MORE will appear on other paths. And this all if you get a direct hit. God help you.

Just as big a concern is induced voltage from nearby strikes. Anything metallic gets energized and conducts to ... whatever it's attached to.

For the most part, surge-suppressor outlet strips don't do much because they can't react fast enough and they rely on the ground in your house - a small, thin wire with lots of curves and bends. You typically don't see a whole lot of damage to phones simply because the telco wires are so small. Electrical appliances can get more of an induced jolt because the wires are thicker. This is why you really should unplug sensitive electronics when a storm approaches. If you hear thunder now, don't touch anything!

Already wrote too much. Be careful!

-Brian

 

[randy41]

i've had an ungrounded steel roof (not tin) on my house for 10+ years now. there have been some nearby lightning strikes that have done various amounts of damage but no structural damage to my house. The worst was when I had an AC fence charger in the basement and a nearby strike blew it across the basement floor and knocked out a few of my electric circuits as well as doing some computer damage. The AC fence charger is in a different building now. the lightning 'liked' the fence charger because there was a good ground.