Thanks alehman for your reply. Further info follows.
Two floors of the building are being used as school for computer sciences courses and installed in those floors called computer labs are 300 units of PCs with servers and routers. Thunderstorm is prevalent in the area hence we want to protect the computers as well as other electrical equipment installed.
Sounds like you are asking about lightning protection. You may want to ask a contractor or even your insurer's underwriter to get some idea of what choices are out there that may lower the building's insurance premiums.
has a very good design guide and equipment descriptions and specifications. You need to consider especially for your voice/data systems that it is critical to provide as much isolation from the system's equipment, power sources and grounding system as possible. Extreme care with regards to the building steel in routing of the downleads from the lightning arrestors is also critical. Hope you get enough information to help.
Standard spiked pole issue that would cover entire building geometry is such that your spike should be on H that will protect entire facility protection geometru is when you project 2H on ground 90 degrees angle
|
|H
----
2H
this is your protection zone. and entire building needs to be inside cone made when you rotate this thing up. If you can not put high spike pole you can chose to put 4 on corners their height should suffice to get the same principle on roof surface (you can put 5th in middle also )
Lets not try to make science from lightning protection
(My professor words and he was doing researches on lightning protection for 20 years) This simple solution and calculus is still the best protection for 99% of purposes. (I am protecting gas power plants on exact same basis)
What you're talking about is an "air terminal" (that's what engineers call 'em) or a "lightning rod" (everybody else).
"Lightning arrestor" is the wrong term for what you want -- an arrestor is more akin to the surge suppressor you plug your computer into than a lightning rod, something to "drain" spikes off the power lines to ground. You'll just confuse people asking to put the arrestor on the roof, when everybody knows that arrestors belong inside your switchgear or on your power pole.
For a lightning protection system, most on this site (including me) would recommend an old-school Franklin type rod designed and installed per NFPA 780 as previously mentioned. Copper is usually the material of choice, unless you have a lot of aluminum on your roof (HVAC equipment, etc), then in that case you'd probably want aluminum.
There's also a new-fangled type that look like Christmas ornaments, known as "early stream emittors" (ESE's) or some such. Most engineers would probably recommend you stay away from those. See
PS -- in the NFPA link above, click the code you want (780) then scroll down to the bottom of the page where in small type they have a link "View the 2004 Edition of this Document". You can't search or print it, but the whole thing is available for your reading pleasure.
PPS -- just realized you wrote "storey" rather than "story", which probably puts you on the other side of the pond. Which means you can forget about a lot of this lightning rod & NFPA stuff.
I don't know much about how the Brits do lightning protection. But the few installations that I've seen, they seem to use something more like flat iron straps run flat along the roof and welded together into sort of a mesh. No vertical elements at all.
Us Americans would all just wave our NFPA 780 books at you and tell you how silly that was, we've known ever since Ben Franklins time that you need a vertical rod. But at least your neighbors wouldn't laugh at you if you put one of those strap systems on -- at least not until your house got hit by lightning just after you got done installing it.
