Lightning Protection for Tall Buildings - Mandatory?

I would check with the local government's building & zoning people. They are the people you have to satisfy, anyway.

news:alt.engineering.electrical is a group that deals more in the power distribution side of EE.

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Michael A. Terrell
Central Florida

Whether it's mandatory or not is irrelevant. Do it anyway. Just put some sharp spikes on the roof, and then either bond them to the steel frame or to some heavy cable to a good ground.

The reason for the lightning rods isn't to absorb a strike - it's to dissipate the charge above the building before it builds up enough to cause a strike; that's why you use pointy ends - the corona drains off the charge, at least right above your structure.

Good Luck! Rich

Building lightning protection requirements vary by province, each with their own idea of which department is responsible. Could be part of the electrical, fire, building codes, or something else completely. I'd suggest contacting one of the companies doing rooftop antenna installations such as Radian or Westower & ask them who does the inspections on the lightning protection systems they install, that should point you in the right direction. If you don't have experience with these systems I'd seroiusly suggest farming it out to someone who does, for supposedly simple systems theres a lot of little "gotchas" in there.

H.

that sounds like a load of crap to me.

If you put ions into the air above a structure that'll attract lightning in much the same way as making it taller would.

Bye. Jasen

Beside mandatory or not, there could be the case when an insurance refuses to pay if not installed...

Rene

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Well, I'll be. According to howstuffworks.com, you're right. It doesn't dissipate the charge, it just diverts the stroke so it doesn't burn the house down. :-)

If you learn something new every day, does that mean I can go back to bed now? ;-)

Thanks! RIch

I inspected some toll booths at exit 99 on I-75 in Florida. They were planning on these little boxes getting hit with people in them. The biggest thing they did was be sure it was a great grounding system.and all the metal was bonded to it.

Yes, lightning loves all kinds buildings here in Florida. It hit one of those old fashioned concrete awnings that was built in a restaurant parking lot for the car hops to stay dry. It also hit the corner of the main building, and the small STL tower in the parking lot and two C-band sat dishes where I lost all the LNAs and the CARS (STL) transmitter.

It vaporized the rebar and the large threaded rods that held the roof panels on the concrete columns. It exploded damp concrete in both structures which went through the various breaker boxes and electronics while destroying almost everything electrical, after some of the old building grounds failed.

It was in Leesburg, and was the original studio and offices of WACX TV, Ch 55. It took weeks to repair all the damage, but I managed to have the phones and lights working an hour after the office opened, then got on the phones to arrange for rental equipment to keep the station on the air.

I replaced the entire ground system, and redid all the cabling into bonded steel conduit. It cost a wad of money, and we were self insured.

On top of that it was my first day as the only engineer on staff. :(

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

This stuff happens when the bonding/grounding is not secure. If you give the lightning a clean path to ground, that is where it goes. I bet they did not have all that rebar tied together and it was just stuck in the wet mud at the top of the columns. At MM99 we probably had close to a half mile of 1/0 copper ground ring along with a bunch of 40' rods around the ring and Ufers on all the buildings, tied to the steel in the roadbed and duct banks. Any significant chunk of metal was bonded along with the normal bonding of "building steel". They did ground testing on every rod and they shot so many CadWelds it was like the 4th of July for a week around there. There were no clamps used on any buried ground connection in the concrete or underground I was surprised at all the engineering that goes into a toll booth and the systems they use. For one thing there is 5 tons of "fresh air makeup" A/C blowing into the booths pulling air from the woods behind the service building. It keeps the CO down in the booth. The duct banks for the electrical, computer and control systems are about 8 feet down to protect them from the traffic. I really didn't have much to look at as an electrical inspector since everything was supervised by an engineer and inspected by about 3 other guys before I saw it. Things were so far above and beyond the NEC it was just a sight seeing trip.

The building was an old restaurant, converted into the studios and offices of a low power UHF TV station. it all happened before I was hired, and from the look of things it had survived several previous strikes without damage, but it appeared that there were multiple strikes that morning and there wasn't time for the copper bonding to cool down between strikes. That was in 1988, and as far as I know, there has been no new damage since then. The studio and control room was bonded with

1/8" * four inch copper, but the multiple power panels were not well bonded, so the ground potential flowed though them and melted them. The main grounding was at the tower and sat dishes. They survived, but the older parts didn't. They were about 40 years old at the time, and probably not up to code for new work. Just a couple miles away WLBE's towers sit in a swamp and get multiple strikes on a regular basis. The engineer has had to replace the conduits to the towers several times because there was so much crap fused to the walls that they couldn't replace the wires, again. When I lived in lake County I could see the lightning heading for the towers, then it would split and hit all of them. Sometimes the strikes were just seconds apart. On the other hand, the new WACX tower in Orange City is 1749 feet of steel that has been hit, but hadn't suffered any damage that I know of. It was over a million dollars to build and it gets annual maintenance where bolts are inspected and replaced, as needed. There is a freight elevator to the top, but I never had the two hours needed to go up, and back down while I was there doing weekly transmitter maintenance.

They had just installed equipment from Innovative Technology

to protect the electrical and data systems at all four sites when I left the station to build Ch 58 in Destin, Florida.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Maybe it was above the NEC at the time, you should see the changes between

1999 and 2002 editions on grounding and bonding, and ampacity.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
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Actual legal requirements do vary some from jurisdiction to jurisdiction. Complying with the requirements in NFPA 70, ANSI/IEEE C2 and similar is often required to buy affordable insurance. I do not have my reference list with me.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller