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Old 06-03-2009, 11:06 AM   #1
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What about lightening rod when they do my roof?


I have several lightening rods on my house - one of my roofing estimates notes:
"No liability can be made for existing condition or functionality of the lightening rod system"

I'll need to ask the roofer, but I assume it means that they will detach and reattach they existing system. Is it worth it to have an electrician come check up on it?

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Old 06-03-2009, 11:53 AM   #2
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What about lightening rod when they do my roof?


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I have several lightening rods on my house - one of my roofing estimates notes:

I hope they all tie back to the system bonding grid IE: Water line and grounding electrode.

"No liability can be made for existing condition or functionality of the lightening rod system"

Thats correct, as a direct strike cannot be dismissed or controlled.

I'll need to ask the roofer, but I assume it means that they will detach and reattach they existing system. Is it worth it to have an electrician come check up on it?
I have little faith in these systems. If it makes you feel better, then call an electrician. A waste of money IMO. Just make sure they are connected as mentioned above (to the whole house bonding grid).


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Old 06-03-2009, 12:08 PM   #3
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What about lightening rod when they do my roof?


Heck, for all I know they attract electricity but they're original to the house, so I'd like to keep them. If the price of copper was still up, I might consider scrapping them to pay for the roof
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Old 06-03-2009, 06:34 PM   #4
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What about lightening rod when they do my roof?


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Heck, for all I know they attract electricity but they're original to the house, so I'd like to keep them. If the price of copper was still up, I might consider scrapping them to pay for the roof
I always joke about helping the neighbor pay for a lightning arrestor system for his house. I figure the lightning would be more attracted to his house and leave mine alone.
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Old 06-04-2009, 12:20 PM   #5
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What about lightening rod when they do my roof?


I have had one one on my house since we bought the place. We got hit a number of years ago and it fried the garage door openers, TVs, Stereo, phone etc. Melted a hole right through the gutter. So did the lightning rod system attract the lighting, not help at all or did it reduce the damage? Who knows? Maybe it would have been worse without it. All I know is that lightning is very loud when it hits your house!
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Old 06-04-2009, 01:35 PM   #6
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What about lightening rod when they do my roof?


In all likelihood, any lightening will skip the house and hit the 200 year old sycamore that SHADES my house, but I kinda like how they look.
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Old 06-04-2009, 04:00 PM   #7
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What about lightening rod when they do my roof?


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In all likelihood, any lightening will skip the house and hit the 200 year old sycamore that SHADES my house, but I kinda like how they look.
You know who would know? Your insurance company. See if they change your rates with/without a system.
Their money is riding on the outcome so they might actually tell you the truth.

"The two most frequently struck tree types are the oak and the elm.[75] Pine trees are also quite often hit by lightning. Unlike the oak, which has a relatively shallow root structure, pine trees have a deep central root system that goes down into the water table.[76] Pine trees usually stand taller than other species, which also makes them a likely target. Factors which lead to its being targeted are a high resin content, loftiness, and its needles which lend themselves to a high electrical discharge during a thunderstorm."

"Lightning protection system design
Considerable material is used to make up lightning protection systems, so it is prudent to consider carefully where a rod structure will have the greatest effect. Historical understanding of lightning, from statements made by Ben Franklin,[9] assumed that each device protected a cone of 45 degrees.[10] This has been found to be unsatisfactory for protecting taller structures, as it is possible for lightning to strike the side of a building. A better technique to determine the effect of a new arrester is called the "rolling sphere technique" and was developed by Dr Tibor Horváth. To understand this requires knowledge of how lightning 'moves'."

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Old 06-04-2009, 04:34 PM   #8
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What about lightening rod when they do my roof?


Although the topic of lightning can be an entire masters or doctorates program, when doing my roof antenna this is what I found. It can likely apply to lightning rods as well.

The reason a roof antenna has to be grounded (an attic antenna does not) is because wind blowing over it builds up static electricity which attracts lightning. I can't say if wind blowing over your roof, gutters, or lightning rods will cause static buildup. By grounding it, as the antenna builds up static electricity by wind it's harmlessly directed to ground decreasing the chance that your antenna will be chosen to be struck vs. say that oak or elm across the way that's not disappating the static electricity as well.

A roof antenna has to be bonded to the breaker panel so everything has the same (I keep forgetting the word... charge or something you want the antenna having the same charge as everything else in the house so you don't shock yourself). That does 2 things, prevents shock and the antenna's grounding rod needs moist dirt. If it's been dry for a long period of time the grounding rod may not be able to release the build-up of static electricity so by bonding it to the breaker panel that eliminates that issue. Though, the code behind why you have to bond an antenna's grounding rod to the breaker panel I'm pretty certain has nothing to do with lightning or dry dirt, it is a good thing.

The next aspect of grounding the roof antenna is that it should be (it may be code) grounded to a grounding rod directly below with minimal bends & curves. This has to do with if the antenna gets struck. All bets are off at this point, the only thing you can do is attempt to direct the strike where you want it to go instead of having it decide to take a shortcut through your house or something. It is certain with lighting rods and properly grounded antenna getting struck is going to cause massive damage BUT the goal is to attempt to direct it to ground ASAP so the damage is not catastrophic or with casualties. Since lightning doesn't take corners very well any bends of the grounding wire to the grounding rod should or must have a large radius, and should be as straight with little bends as possible to the ground rod, but expect serious damage. Not all the lightning is going to choose that path and even the smallest fraction that doesn't will cause massive damage.

Okay, you're probably bored. Things to think about, are your lightning rods connected in as straight a line as possible to grounding rods burried below? Are they connected to the breaker panel? Is your soil/dirt dry?

This doesn't discuss lightning feelers... and all I know about is a small bit of why a roof antenna has to be grounded and how best to do it... I really don't know about lightning rods but perhaps some light was shed. Lightning is so vast this hardly scratches the surface.


Last edited by Piedmont; 06-04-2009 at 05:04 PM.
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