lightning protection for light poles 6

[oliupe]

I have a job where the customer insists in providing aerial points to each of the 35' concrete poles used for lighting a parking lot in a large shopping center. I have a ground rod in each of the poles. Is this extra step of installing an aerial necessary? Advisable? Good judgment? I have not been able to find information under any of the lightning protection companies or pole manufacturers. Can anyone offer an idea?

Thanks,

Octavio

 

[peebee]

Where are you geographically, and at what elevation? I'd recommend a lightning risk analysis per NFPA 780 - Lightning Protection Code.

In general, though, the concrete would require more protection than metal poles. Concrete tends to suck up water. You hit that pole with lightning, and the water turns to steam, and your pole violently turns to dust. Metal won't do that, it will take the stroke without damage.

If you are in a vally, surrounded by tall buildings, in an area where you seldom get storms, though, then you probably don't even need any protection.

By the way - what is the intent of installing a ground rod at each pole? Lightning?

 

[oliupe]

THANKS FOR YOUR REPLY. I AM IN SOUTH FLORIDA, ELEV = +0. THE GROUNDING ROD IS A LOCAL REQUIREMENT (USELESS), THE CONCRETE POLES ARE EMBEDDED 7' ON THE GROUND. YOUR COMMENTS ARE MORE THAN WELCOME
THANKS

 

[cuky2000]

The NFPA Standard for Installation of Lightning Protection System NFPA 780 1997 edition were withdraw because “deficiencies and questionable scientific and technological validity”.

The NFPA Council discussed to issue or not the 2000 edition of NFPA 780.

Caution using this standard is advised.

 

[busbar]

Wow cuky'! A hot potato for certain. The NFPA seems in a total, uncharacteristic uproar over 780 {and ... 781 maybe} [I've retired so I'm out of the loop, lately.]

http://www.nfpa.org/Codes/NFPA_Codes_and_Standards/List_of_NFPA_documents/NFPA_780.asp

See entries at "Additional Information about this document:" {Ben Franslin and 1750 are even referenced!}

 

[sunilji]

You mentioned the height ofthe poles but not of the surrounding structures, If you have significantly taller structures in the vicinity ( Radio Mast, Skyscrapers, Overhead water tanks etc.) it could provide a cone of protection to obviate the use of individual air terminals.
Otherwise, you could alternatively opt to construct one such large mast/tower with a spike on the top, an lightning event counter at the bottom and locate it such that it provides a cone of protection to the shopping center as well.
By the way I have seen municipal area lighting masts (50'+) and holding high mast flood lights ( 6 x 400W HPSV )carrying a lightning spike on top.
Finally visit

http://www.furse.com

and call for their handbook on lightning protection

 

[SooryaShrestha]

The size of the pole with 7' under the ground means it is used not for very high voltage. I think the use of lightning safety for low voltage using Franklin rod or otherwise will be only cosmetic, as in such lines if the lightning strike takes place, because of lower insulation level there will be backflashover.So in lines where it has been used will not be of much help. The only way for safety is to have low earth resistance by several of standard or specific means.

 

[cuky2000]

Lightning protection technique are in proccess to be re-discovered and standards updated based in recent lightning data and new knowledge in this subject.

Since FL is one of the most active keraunic zones in the US, I suggest to Oliupe to take additional step to properly choose the most effective technique and have proper tools to discuss with your client any action that will have budget impact in the installation.

Sunilji, you mention “cone of protection”. We should be aware that this method provide partially protectiondepend of the angle of prtection(~90 for H<100m). The rolling sphere method is more accurate providing more than 95% level of protection.

There are other emerging technologies and method that promising to address some of the deficiency of the NFPA 780.

The enclose article is recommended for those that have curiosity in new ides regarding lightning protection, specially in critical facilities.

http://www.lightningeliminators.com...f Advanced Lightning Protection Technolog.pdf

I hope this information help to bring more light in this subject.

 

[BJC]

Oliupe.
I would consider the leagle consequences of this whole project. It's a sad state of affairs but there is a lawyer under every rock these days.
If you put point's on all the light poles you are in effect designing a lightning protection system. If the poles are to far apart to cover the parking lot adequately then it's not a good sytem. The owner wanting points on every pole doesn't make it a complete system. He is in effect designing the system for you ( I assume you will be the engineer of record ) and you could be at fault if it doesn't work. The public depends on you as a PE to put their instrest first ( when it may confict with the owners need to save money).
When I have dealt with lightning protection systems I have hired a specialist to design and install a complete system. Twenty years ago that was someone who had a masters license as issued by UL (I think).
Now the state of the art has advanced considerably. I would find out what kind of systems are approved by insurance carriers like the Factory Mutual or The Hartford. Have someone who can meet their criteria design and install the system.
Someday there may be something like a farmers market in the parking lot. The rain starts and people huddle under a shelter somewhere between two light poles. BOOM! a stroke takes them all out. The lawyers will be there like flys on a t___. Not only will they go after every cent you have you could face criminal charges as well ( you need a real lawyer to tell you that, depends on the laws in Florida).

 

[jbartos]

Suggestion: Any high structure, especially with electrical installation, is advisable to provide with lightning protection. The concrete poles are not conductive as metallic ones, however, when they become wet, they can conduct somewhat. The electrical instalation probably has some connection or proximity to the earth ground at some point. Therefore, the lightning protection is under consideration and posing a concern to have it. In addition to the NFPA 780, there are references cited therein. Also, the Standard Handbook for Electrical Engineers by Fink and Beaty, 14th Edition, McGraw-Hill, 2000 has Section 27 Lightning and Overvoltage Protection. It states that the lightning devices help in reducing damages due to lightning.

 

[peebee]

As far as I know, the issues with NFPA 780 have all been resolved. The proposed NFPA 781 was rejected, and it was affirmed that there was overwhelming evidence in support of NFPA 780.

The issues were raised by the manufacturers of early stream emmission (ESE) lightning protection systems. NFPA said there was no evidence that ESE's worked; the manufacturers came back and said there was no evidence to support 780, either. However, over a long review period (~2yrs?), SEVERAL engineering reports were submitted indicating the effectiveness of 780-type installations. The ESE guys submitted some research, too, but NFPA has not recognized ESE's as being any more effective than traditional Franklin-type air terminals.

 

[busbar]

This sort of &quot;incipient scandal&quot; seems to resurface occasionally in the electrical business. Exampli gratia, rubber- {thermoset} versus vinyl- {thermoplastic} wire insulation and, steel versus plastic raceway were heated issues in their time.

 

[Polecat]

Oliupe:

This note may be a little too late for your project, but here it is for what it's worth.

First, to address JBARTOS' comment above. With all due respect, he couldn't be more mistaken about the conductivity of concrete poles. With an abundance of steel strands buried within, it is a natural lightning rod just waiting to be struck. I have found myself in a witness chair answering questions about this very point. You don't want to go there.

Since you're in South Florida, then check with FPL's distribution engineering dept. Their street light standard has a #6 copper ground embedded in the pole. As mentioned, the pole itself will act as a lightning rod, given the amount of steel strands cast within. A lightning bayonet on top is not going to add much to its protection unless you strap a huge conductor to the outside of the shaft in hopes that it will divert the charge more directly to the ground instead of traveling thru the pole. But now you are really getting into a grounding system as others have mentioned.

Let me know if you need further info about concrete poles.

http://www.spiraleng.com

 

[oliupe]

THANKS FOR YOUR REPLY, IT WAS REALLY HELPFUL AND REINFORCED WHAT I ORIGINALLY HAD IN MIND. AGAIN, THANKS.
OCTAVIO

 

[cuky2000]

Enclose please find an article that suggest how to calculate the self and mutual surge grounding Impedance in concrete pole with vertical conductors.

Beware that this information could not replace any code or standard. However, I find this is a good information that could contribute to understand better the interaction between concrete poles and ground electrode in the event of lighting strike.

http://www.ipst.org/TechPapers/2001/IPST01Paper028.pdf