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Old 06-01-2007, 08:46 AM   #1 (permalink)
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Lightning and Metal Buildings

Does anyone have any ideas on the safety of a metal building on a concrete pad during a lightning storm?

I have always heard the tale of lightning coming up through a basement floor etc. and wanted to get the opinions of some of you with metal buildings.

I would think that lightning rods and such aren't going to do anything - but I don't know.

Thanks!
Chris
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Old 06-01-2007, 02:40 PM   #2 (permalink)
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Originally Posted by jeepnchris View Post
Does anyone have any ideas on the safety of a metal building on a concrete pad during a lightning storm?

I have always heard the tale of lightning coming up through a basement floor etc. and wanted to get the opinions of some of you with metal buildings.

I would think that lightning rods and such aren't going to do anything - but I don't know.

Thanks!
Chris
Electricity will always take the path of least resistance. this means that the electrical current will travel through the steel beams and skin much easier than through the air space inside the building. so unless you are standing on the top of your building holding a golf club up in the air then you are pretty safe inside.

Wayne
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Old 06-01-2007, 04:10 PM   #3 (permalink)
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Electricity will always take the path of least resistance. this means that the electrical current will travel through the steel beams and skin much easier than through the air space inside the building. so unless you are standing on the top of your building holding a golf club up in the air then you are pretty safe inside.

Wayne
Thanks! Maybe you answ. it, my question is if I am inside the building am I safe from Lightning? Will the lightning be diverted by the metal structure and not harm the people inside (don't touch the walls though ).

Chris
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Old 06-01-2007, 04:25 PM   #4 (permalink)
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Thanks! Maybe you answ. it, my question is if I am inside the building am I safe from Lightning? Will the lightning be diverted by the metal structure and not harm the people inside (don't touch the walls though ).

Chris
Yes you will be safe. your hair will stand up and there will be a tremendous boom. but you will be ok as long as you are not touching the side of the building and even then you will probly be fine....just not a good idea to test probly IMHO.

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Old 06-01-2007, 04:29 PM   #5 (permalink)
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Yes you will be safe. your hair will stand up and there will be a tremendous boom. but you will be ok as long as you are not touching the side of the building and even then you will probly be fine....just not a good idea to test probly IMHO.

Wayne
LOL - thanks! I am not really fond of trying my luck by touching the building. So you think the concrete floor is safe as well?

Chris
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Old 06-01-2007, 04:56 PM   #6 (permalink)
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You still want a proper lightning rod system - that will then direct the electricity rather than blowing out all your electrical equipment and damaging your building.
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Old 06-01-2007, 05:00 PM   #7 (permalink)
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You still want a proper lightning rod system - that will then direct the electricity rather than blowing out all your electrical equipment and damaging your building.
I don't see why lightening would attack your electrical circuits in a steel building. The path of least resistance is through the building structure to ground, period.

As long as the building structure itself is well grounded (and I dunno if bolting it to a concrete pad is good enough, or if you need several deep ground rods, or what) it IS a lightening rod.
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Old 06-01-2007, 05:10 PM   #8 (permalink)
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I know when I used to do HVAC work on the air force base here, the F-16 hangers which were metal had a cable type lightening rod system with little "antennas" for lack of a better word all over the roof. Every piece of equipment up there and high points had a little 2-3 foot antenna on it all interconnected with a series of thick wires. I'm sure they went down to some non critical point away from the building in case they were needed. Of course they were sitting on 3 F-16's at a time and tugs full of jet fuel, so they were real careful about sparks. You even had to touch a copper ground pad anytime you went out into certain areas, all hand tools, nothing power or pneumatic to create a spark.

I think you're probably more likely to get a blowjob from Posh Spice than to get stuck by lightening and killed working in your steel shop.
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Old 06-01-2007, 05:30 PM   #9 (permalink)
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I don't see why lightening would attack your electrical circuits in a steel building. The path of least resistance is through the building structure to ground, period.

As long as the building structure itself is well grounded (and I dunno if bolting it to a concrete pad is good enough, or if you need several deep ground rods, or what) it IS a lightening rod.
My building is connected to Wood on both sides - not concrete. The new building is 30' by 40' and has wood on the sides where the metal walls connect to. The pad is inside of that with wood decking supporting the metal structure. How do I figure out the load for the lightning protection - or better yet does anyone have a figure that would work? I want to be safe - mainly for my wife and my friends. We own a wheeling park as well and a some people may be in there during a storm.

Thanks!
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Old 06-01-2007, 05:39 PM   #10 (permalink)
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I think you're probably more likely to get a blowjob from Posh Spice than to get stuck by lightening and killed working in your steel shop.
LOL - I wish that was true LOL - maybe I don't because my wife is looking over my shoulder In all fairness I would rather be with my wife then with Posh. Posh is hot though!

Chris
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Old 06-01-2007, 08:26 PM   #11 (permalink)
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I would suggest putting a 10 foot ground rod in at each corner and attach it to the metal walls with at least a bare #2 copper wire as a minimum. This will give the lightning a easy path to ground rather than through the building wiring which would be the next easiest path. Seen a lightning damage a few times in ungrounded structures(30 years as an electrician). It will take strange paths if no easy one exists.
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Old 06-02-2007, 05:26 AM   #12 (permalink)
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As a Building Inspector have done many inspections on metal buildings. Not knowing how your footings and main structure beams were installed. I would say follow the guidelines below. I can say for all the metal buildings I've seen, the main structure steel columns base plates/anchor bolts are connected to the footing rebar in some manner and hairpins hooked at the bolts running across a rebar pad grid. Does that make any sense? Hard to explain. Anyway this creates a perimeter ground for the building with one 5/8"x8' ground rod connected to one base plate of a steel column base plate. On small 30'x40' buildings the Engineer asked for one ground rod and on larger buildings the Engineer wanted a ground at each plate.


UNIVERSITY OF NEW HAMPSHIRE CONSTRUCTION AND RENOVATION STANDARDS SECTION 16170 - GROUNDING AND BONDING
PART 1 - GENERAL

1. Grounding shall be done at the service entrance equipment in each building by connecting the neutral bus of the service equipment to a grounding electrode, street side of the water meter if the water service is a metal water lines. The metal cabinet of the service equipment must also be connected to the neutral bus in order to provide equipment grounding.

2. If a metal water line does not service the building other means of grounding shall be applied. Each building must have a grounding electrode for its service. The proper grounding electrode system will be determined by the Engineer/Owner and will comply with all applicable codes.

3. Under no circumstances is the electrical neutral to be used as an equipment ground beyond the point of the service entrance equipment.

4. Under no circumstances is the electrical neutral to be tied to the equipment ground except as stated above.

5. All raceway, conduit systems shall have an equipment grounding conductor pulled in with the other conductors beyond point of service. Each joint and termination must be tight so that there is electrical continuity.

6. All junction boxes, pull boxes, switch boxes, outlet boxes, etc., shall be bonded to the equipment grounding conductor by means of a green bonding jumper and screw.

7. All metal buildings shall be grounded at each major structural steel column to an exterior grounding ring.

8. Care shall be taken not to create a parallel path to the neutral conductor by any other means of grounding.
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Old 06-02-2007, 06:19 AM   #13 (permalink)
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7. All metal buildings shall be grounded at each major structural steel column to an exterior grounding ring.
This is the one that will keep you safe in a storm. The others will keep you safe when your electric system takes a dump or will help reduce the damage to the equipment when a storm comes through.

Chris, are you building it out in the field? If you are up in the trees on your existing pad it shouldn't be a big deal but I would still put in grounding rods.
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Old 06-02-2007, 06:56 AM   #14 (permalink)
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Just get a lightning rod you will be alright.
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Old 06-02-2007, 06:59 AM   #15 (permalink)
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This is the one that will keep you safe in a storm. The others will keep you safe when your electric system takes a dump or will help reduce the damage to the equipment when a storm comes through.

Chris, are you building it out in the field? If you are up in the trees on your existing pad it shouldn't be a big deal but I would still put in grounding rods.
It is located where the canopy was. I built out on the sides of the pad and put the building there.

The building looks likes this (but smaller):



I was going to take the guys suggestion and run a grounding rod on all four corners. Will that be enough? Since the building is kinda a "unibody" there really are no columns.

It is also temporary - at least that is my story

For the power I was going to put in a small sub panel off of the main houses panel.

Chris
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Old 06-02-2007, 08:11 AM   #16 (permalink)
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Dang Chris, That is gonna be saweet. Bet you are gonna miss the pup-tent shop.

I will check it out on my next visit.
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Old 06-02-2007, 08:37 AM   #17 (permalink)
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If you're still in the design stage, build in an Ufer ground in your concrete foundation and slab. If it's already there, it's too late.

Also see if you can get a copy of NFPA 780, the national lightning protection standard. Lot's of good info there.

If you want MIL-grade lightning protection as one poster described with the F-16's, then PM me a snail mail address and I'll send you a CD with MIL-HDBK-419, parts 1 and 2. You'll be bullet-proof then.


One comment: one ground rod does not a lightning protection system make (see -419 part 1 as to why). Use many, tie them together, use large conductors. If you're going to do it, do it right and over kill it.

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Old 06-02-2007, 12:01 PM   #18 (permalink)
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One comment: one ground rod does not a lightning protection system make (see -419 part 1 as to why). Use many, tie them together, use large conductors. If you're going to do it, do it right and over kill it.
Thanks for the offer. Do you think one on each corner is enough? Maybe 6? 8?

Chris
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Old 06-02-2007, 03:27 PM   #19 (permalink)
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Thanks for the offer. Do you think one on each corner is enough? Maybe 6? 8?

Chris
Much better, you're thinking as if you've read 780 et al. 6-8 *should* work well unless you're a couple feet over bedrock.

No one can answer if "X number" is good enough without a test; but it's far better than one or two. I have 8 around my house, plus the copper water pipe plus the swimming pool ground rod.

Good luck.

Al
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Old 06-02-2007, 04:16 PM   #20 (permalink)
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Much better, you're thinking as if you've read 780 et al. 6-8 *should* work well unless you're a couple feet over bedrock.

No one can answer if "X number" is good enough without a test; but it's far better than one or two. I have 8 around my house, plus the copper water pipe plus the swimming pool ground rod.

Good luck.

Al

Actually rock is just under a small layer of dirt. I could not tell you what kind of rock but I am thinking granite - I am located in Crozet, VA (central virginia - base of the Blue Ridge). Does that mean more ground rods?

Thanks again!

Chris
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Old 06-02-2007, 06:56 PM   #21 (permalink)
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Chris, if you can drive 8 foot rods into the ground vertically, you might be ok. Again, more is better, but I wouldn't obsess over it.

Another thing: Make sure they are outside the drip line, i.e. they are not sheltered from rain by your roof. Water makes a big difference in the resistivity to ground for grounding systems; and what you're trying to do is lower the resistivity as low as possible. Also make sure each ground rod is at least it's length away from the next ground rod. Two ground rods one foot apart (like the OEM rods on my house) aren't two rods, resistance-wise.

In the work that I do, and for most industrial and military construction, 10 ohms is the bare minimum for a good grounding system. One of my (8) rods measure over 750 ohms (installed by the house electrician when the house was built) and one installed by me measured 57 ohms +/-. NEC (Nat'l Electric Code, aka NFPA 70) says 25 ohms is the minimum, but doesn't say anything about how to achieve it or measure it other than provide acceptable grounding methods.



War story: in one electrical transfer facility on one of our sites, the electrical utility installed around 85 twenty foot long, 3/4" diameter ground rods in a typical IEEE 2000.1 design for transfer stations. They measured the resistance to ground and got over 75 ohms.

They ended up drilling two ground wells +275 feet deep until they hit ground water. That's two wells with 6" steel pipe over 275 feet; in other words, a lot money. We ended having to do the same thing except we had to drill about 20 or so wells. Life when you're hauling around 45k lbs class explosive.

Good luck.

Al
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Old 06-02-2007, 07:17 PM   #22 (permalink)
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Hire a lightning protection contractor. They will design a UL listed system, and when installed properly, can also reduce your building insurance premium.

Just slapping shit together haphazardly won't do, and adding a bunch of stuff just because it seems like a good idea can be wasteful (time and money)

Do the right thing, and give one of these contractors a call (not the tree guys)

http://maps.google.com/maps?hl=en&um...e-results&cd=1

Albin's given you some good parameters, but you still need help to do it right.

The same advice holds true for all of you that live in states with a high lightning strike potential. Florida is #1 in the union, followed by Texas at #2.

A little more information can be found here:
http://www.lightningsafety.com/index.html
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Old 06-02-2007, 07:54 PM   #23 (permalink)
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Electricity travels on the outside of metal structures. it's the same reason you are safe from lightning in your car,because the electricity flows on the outside of the metal skin. it is a myth that you are safe because of the rubber tires. Apply that same reasoning to a metal building. atleast that is what I have been taught in my college physics classes.
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Old 06-02-2007, 07:59 PM   #24 (permalink)
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Yes, electricity does travel on the outside, it does the same with wire as well. Good for you, paying attention in class.

You're protecting your property, as well as yourself with a proper lightning protection system.

I've seen it blow holes in roofs, make electronics explode like in a movie, cook entire electrical systems in buildings. It's serious stuff. 100 million volts does a hell of a lot of damage..
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Old 06-02-2007, 09:09 PM   #25 (permalink)
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I've been struck by lightning. It's not that bad.

Quit being a pussy.
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