Metal Roofs

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A/A Fuel GTX

A/A Fuel GTX

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Electrician
With the increasing popularity of metal roofs today, I was thinking that it may be a good idea to bond the roof to the GES just like antennas and lightning rods. Any thoughts and if so, what would be the proper termination?
 
petersonra said:
What makes you think bonding it is going to attract lightning?
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Anything metal up high that is grounded is more likely to attract lightning than something that is not grounded, IMO.


To the OP --Lightning rods supposedly take lightning and direct it to a safe path but they are higher than the house and designed for that. The Antenna would use the cable wires to go back thru your TV instead of to a safe exit.

The fact is lightning will do what it wants and I am not convinced about the use of lightning rods either.
 
Dennis Alwon said:
Anything metal up high that is grounded is more likely to attract lightning than something that is not grounded, IMO.

The fact is lightning will do what it wants and I am not convinced about the use of lightning rods either.
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So what benefit would one get by bonding the metal roof to the GES and increasing the chance of a lightning strike?

I am not convinced it would increase the chances of a strike, nor am I convinced it would serve any beneficial purpose in the event of a strike. I sure as heck don't want to increase the chance of a strike.
 
Frankly , I think their opening a can of worms, will everything be required to be attached to a GEC if this one aspect is required?

What about metal siding or even awning, granted both are not in vogue anymore but where would this metal to bonding stop?
 
The house in question is wood frame construction with a steel roof as well as steel siding. The siding and roofing is quasi bonded anyway via the intersystem bonding terminal mounted to the side of the house. I should probably quit pondering too deeply into certain things:blink:
 
I?ve thought too long about it?

A good refreshing read is really starting from Article 250.4 and reading on! :)

The answer already exists as asked, I?m incorrect your answer is Article 250.4(A)(5).

If ones work doesn't touch it, is how I've always worked. :ashamed1:
 
lightning rods are there to take lightning hits!

lightning rods are there to take lightning hits!

For best understanding why grounding the metal roof is a bad idea, google lightning protect methods and study up on it... You will find grounding the metal roof is just like moving the earth up HIGHER in the sky and so will indeed attract a lightning hit - lightning will go for the highest grounded point.....

On the other hand, a lightning rod is a special device made with as sharp a POINT on its vertical end as possible. this point DISCHARGES the static build up in the air and runs that static to ground thru the bonding wire. this eliminates the voltage difference between that point in space and the clouds with the lightning, thus eliminating the ionization of the air and thus preventing the strike in the first place. these rods are not there to take lightning HITs, just to discharge the voltage so it wont happen to begin with. You may have seen this in action on high radio towers where they have a pointed discharge rod attached then to a large metal sphere - when the static builds enough you can get lucky and watch the ball shooting off lightning into the air as it discharges like a whatchamacall it - vandegraff - thingy.

LOTS of difference between these two things!

Now if you want to talk about adding lightning rods to the highest points of the metal roof and bonding THEM to ground, now your on the right path....just like the 1920 metal roof barns of old....

that said, anyone with a metal tower for their ham radio antennas should have at the highest point a sharply pointed metal rod to discharge the static and prevent the antenna from attracting lightning. I have not had a lightning strike on my towers in the last 40 years - they have always had a sharp pointed grounded metal thing on the top *(usually in the form of a 5/8 wave 2 meter antenna).

oops: left out the NOT in title but edit won't let me add it....
 
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mike_kilroy said:
For best understanding why grounding the metal roof is a bad idea, google lightning protect methods and study up on it... You will find grounding the metal roof is just like moving the earth up HIGHER in the sky and so will indeed attract a lightning hit - lightning will go for the highest grounded point.....
Click to expand...

So you figure a lighting bolt that travels a few miles across the sky will suddenly take a turn to find a metal roof that is 15' higher than the earth around it?

I find that unlikely.
 
lightning is mighty unpredictable, yep. recall the soccer players a few years back in IIRC CO that got hit by lightning from a clear sky - the storm cloud was 7 miles away......

why not stand under a tree in the middle of an open field?

likewise why make the low resistance ground a metal sheet 40x60 foot square, higher than other surrounding grounds? If you were lightning and wanted the lowest impedance path to ground, what would you hit? I would go for that big metal high up target in a heartbeat....just doesn't seem like a good bet to take.
 
mike_kilroy said:
lightning is mighty unpredictable, yep. recall the soccer players a few years back in IIRC CO that got hit by lightning from a clear sky - the storm cloud was 7 miles away......

why not stand under a tree in the middle of an open field?

likewise why make the low resistance ground a metal sheet 40x60 foot square, higher than other surrounding grounds? If you were lightning and wanted the lowest impedance path to ground, what would you hit? I would go for that big metal high up target in a heartbeat....just doesn't seem like a good bet to take.
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We will remain in disagreement here.

To a lightning bolt traveling through the high impedance of air the roof of any structure intentionally grounded or not will be a much lower impedance path.
 
ok, we'll disagree. actually dry air has an impedance of 377 ohms, not particularly high, especially when the voltage difference between the cloud and earth is in the millions of volts. so taking 0 ohms up the 25-30' above the surrounding ground seems significant to me. but when lightning strikes, the ionized air is no longer 377 ohms but 0. height above ground is one of the main reasons one place gets hit vs another.
 
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