Lightening Protection for a building 4

[TomFitz]

Recently I took a position as a facility operations manager and have observed many of the lights being blown during storms and lightening for the past two weeks. Also have had to reset many of the pumps and air handlers in the building, and had one pump burn up. The lightning suppression system in the building is a bonding system, and is not isolated from the building. Wouldn't this direct the lightning through the structure and the equipment. My discipline is not electrical but I would imagine that the lightening protection would be better if insulators were installed on the rods and isolated from the building..
Any suggestions appreciated..

 

[dpc]

It's more likely that you are seeing surges coming in over your incoming power and telecom services. You should make sure that you have adequate surge protection on the incoming power, telephone, and data lines.

The lightning rods and down conductors can be insulated from the building structure, but must be bonded to the building grounding system at some point, per the NEC.

In the case of direct lightning strike on the building, the lightning probably traveled 50,000 feet through the air, so any insulators installed would be of minimal value anyway.

 

[resqcapt19]

I believe that NFPA 780, the lightning protection code, requires bonding of grounded items within 3 or 6 feet of any part of the lightning protection system. This is to prevent "side flashes" between the lightning protection system and other grounded objects. Just bonding at one point will not prevent this problem because of the large voltage drop on the lightning protection system conductors when they are doing their job.

 

[Comcokid]

In addition to the typical 'conduction' means of lighting protection that is covered by codes, practices and regulations, there is the other physical aspects of lighting.

Lighting is a high current/high voltage discharge that ocurrs over a long path. As such, even a nearby lighting strike produces a lot of EMP (electromagnetic pulse) that radiates and can be picked up by the longer wires in a building. Building wiring routed through conduit is shielded by the conduit and is low impedance and unlikely to have a significant voltage induced on it. However, wires for computer connections, alarms, control circuits, etc are usually strung around in a building without conduit and with no more than a foil wrap for shielding. These can pick up the radiated pulse (especially if they are long) and channel it right down to the interface circuits at either end - frying them or upsetting the control electronics.

Are you air handlers and pumps controlled by lower voltage control lines? Did your pump burn up because the controls turned it on with no load, or with a valve in the wrong position? Or are you power items being truly directly overloaded by the strike getting on your building power?

 

[VEBill]

Comcokid makes a good point about induced EMP. There is also the reaction of the charge carriers in the ground. In other words, in addition to the induced EMP from the obvious lightning bolt, there can be a similar EMP from the ground current. Although it makes sense that the ground currents would be more distributed and thus less than the bolt, they may also be MUCH closer to your sensitive low voltage wiring.

 

[7anoter4]

I agree with dpc "You should make sure that you have adequate surge protection on the incoming power, telephone, and data lines". Also you have to check the lightning protection according to NFPA 780 that means: lightning rods, a roof ring and at least 2 down-comer of suitable grounding conductors [it is indicated to be laid outside the building and connected to the all exterior metallic parts close to these grounding conductors],and keeping a distance of 2 feet from the foundation, grounding rods should be connected to the down-comers. See the link for more information:

http://www.lightningsafety.com/nlsi_lhm/lpts.html#bonding

Regards

 

[7anoter4]

You may also purchase the NFPA 780 [if NFPA is the legal code in your country]:

http://www.nfpa.org/catalog/product.asp?category_name=&pid=78097

 

[TomFitz]

Thank you all for your responses and giving me a better understanding of lightening protection.

I have contacted the contractor to test and make sure that I have adequate surge protection on the incoming power, to all my equipment.

Thanks again...

 

[Sparkyman]

Good answers above, well deserving of the stars awarded.
Just one point Tomfitz (apologies if you think I am a pedant, but spelling and grammar in engineering is important to me) there is no e in the middle of lightning.

 

[epepito]

Maybe his stuff is lightening and grounding out as it floats into the air. Sorry I couldn't resist. Pedant, that is a good word, are you a teacher? I mean damn you're pretty heady for a guy named Sparky. Oh and Tom, I might have made the same mistake, but not now thanks to Sparky.

 

[eststation]

I know that the NEC changes every 3yrs but does the NFPA 780 do the same? Is the 1997 issue the most recent one that has been issued?

 

[resqcapt19]

There was a 2004 edition of NFPA 780 and the current edition is the 2008 edition. It appears that the next one will be the 2011. Proposals for the 2011 edition are due 12/1/08.

 

[peebee]

You can view all NFPA codes for free online, including NFPA780, at nfpa.org. Click "List of NFPA codes & standards" at the left of the home page, then click the code you want to view. At the bottom of the page for NFPA 780, there are links to view the 2004 & 2008 editions. Pick whichever you please.

If this is the first time you've viewed the free online codes, you will be prompted to enter your email address and pick a password. Not a bad deal for free access to all NFPA.

You cannot search, print, or download with this free access. But hey, it's free.