Lightning Grounding of Mechanical Equipment

[ClausB]

We are locating new refrigeration equipment on the roof of an existing manufacturing building. The building does not presently have a lightning protection system. The owner has questioned that since the new refrigeration equipment is the highest point, does this need special grounding for lighting protection. My opinion is no, since it is tied to steel structure above the roof which is connected to building steel and the entire systems is grounded and additional grounding is unnecessary, short of putting in an actual lighting rod/protection system.

Opinions or comments?

-Claus

 

[davidbeach]

It depends. Where are you, what is the threat level from lightning?

 

[lile001]

We have installed lightning protection components on tall buildings where the cooling tower is the tallest thing on the building. Although it is connected to building steel, you'd rather have a little control over what is struck first and where the current travels. (Not that lightning can be controlled, after all it can jump 10,000 feet, what's another inch?) You take into consideration the importance of the building (this was a hopsital) the lightning frequency (Houston, gets a lot of storms) and the height of the building (several stories). What you are trying to achive is that everything is bonded, pointy lightning rods are located at the tops of tall objects to dissipate charge, and of course you have a good conductor to ground.

I also ask the client. If they want a lightning protection system I put it in, since it is mostly optional.

If the whole building is not protected, then it would be silly to protect one cooling tower by itself.

 

[VEBill]

If the units have any lengthy runs of low voltage control wiring that could possibly be subjected to lightning-induced 'surges', then I'd have a long think about how to make sure that the low voltage circuits are protected. After all, if the control board is just ever-so-slighly damaged, then the whole unit is still just as non-functional.

The low voltage circuits are typically much more delicate than, for example, the AC supply side.

For example, if the control lines run parallel to the lightning ground path through the structure, then you might have to replace the control circuits at both ends with every stroke.

 

[ClausB]

The location is in New York, midway on the boarder with PA. The maps I see showing lightning strikes indicates this is a low incidence area, but it only takes one accurate strike. No controls on the condenser; those will be in the MCC, below; only power wiring above the roof level. Refrigeration control panel has surge protection. I think we will address this as lile101 posted that the protection is not required but if the owner feels more comfortable we can get a UL protection installer to provide a price.

Thanks for the info. One project I worked on previously had the elevator control panel and a chiller control panel fried by a nearby lightning strike. The chiller ended up destroying itself. Finger pointing all over the place as to who's insurance company owned the responsibility for that since the project was in the final construction phase and not turned over to the client at the time. That was a close strike, not direct.

 

[rbulsara]

Depends on many variables, but in general you do. You do not want your machine to be a single object attracting lightning. One misconception is that the lighting protection (LP) system diverts the lightening current. if lighting strikes. The fact is that multiple pointed air terminals in a proper LP system helps "dissipating" the electrical charge in the nearby atmosphere so that the voltage between the ground and a charged cloud/air will not reach a point of a breakdown (flash) point so it will not let a lightning strike occur. Your blunt shaped machine is no substitute for LP terminals. In fact the machine acts as elevated earth mound that is closer to the charged air, instead of dissipating the charge earlier, it will act as closest path for a lighting to strike. And trust me when a lighting strikes nothing protects it.

 

[VEBill]

"...when a lighting strikes nothing protects it."

Although often correct, there are counter-examples. For example, antenna towers for AM radio stations (where the tower IS the antenna). These are often hit repeatedly, year after year, without any damage whatsoever.

Lightning protection is simply another design requirement. 'Is it cost effective in this application?' is another question.

 

[l3city]

Check NFPA-780, Regards

 

[rbulsara]

VE1BLL:

Tall towers have more than enough metal to carry the lightnig surge, even direct hit, safely to ground, as they are all metal and interconnnected elements provide multiple path to the ground. Normally there tower are so tall that lightning current finds a directly path to the ground and generally have no objects/buildings nearby to jump to. Standards generally allow metals thicker than 3/16" to be substituted for lightining conductors, without burn through. Towers structure far exceeds these and trust me they are very well grounded as well. Also shart object on top of them do try to disssipate charge, but if a large charged air volume/cloud is formed, a single peak cannot keep up and eventually lead to a lightnig strike. I would bet more instances of lightining are avoided then they are formed due to such towers.

Visit website of LPI (lighting protection Institute) and read some of their FAQ.

 

[waross]

I was always under the impression that the purpose of a properly designed lightning protection system was to avoid a lightning strike, rather than to withstand it.
Of course, the system is also designed to withstand a strike, if the strike cannot be avoided, but the first purpose is avoidance.
respectfully

 

[rbulsara]

waross:

That is true. System with multiple air terminals aovids them almost all the time. Single terminals like a tower may not always.

 

[geekEE]

This site shows photos of grounding on a tower antenna

http://www.copper.org/applications/electrical/pq/casestudy/kgbi_station_A6082.html

 

[VEBill]

rbulsara: "Towers... ...trust me they are very well grounded as well."

In attempting to be brief, I apparently failed to make my point with sufficiently clarity. For this I'm sorry and I'll try again.

I had specifically selected the example of "antenna towers for AM radio stations (where the tower IS the antenna)", NOT general run-of-the-mill (grounded) towers.

I had used the specific example of AM radio station antenna towers because I know that some (and I think most) AM radio station antenna towers are not grounded at all (being fed at the base). They are in fact carefully insulated from ground (mounted on insulators) and then connected directly to the transmitter room.

There is, of course, a lightning discharge air-gap at the base of the tower. This is just one part of the overall, specified, designed-for-the-purpose, Lightning Protection System.

My point is that a lightning strike is a normal part of business for some systems and can be dealt with.

Another example is aircraft. On average, a typical aircraft is hit about once per year. The most common damage is: none at all. It isn't luck. It is the result of careful engineering directed exactly towards that very outcome.

 

[VEBill]

waross: "...purpose....to avoid a lightning strike..."
rbulsara: "That is true."

The last that I had read was that the 'jury was still out' (and that's being extremely generous) about the theory that lightning could somehow be prevented. But, out of interest and trying to be open-minded, I checked out the LPI FAQ to get the latest information:

http://www.lightning.org/?page=faq

<QUOTE> If you check our website under Non-Compliant System information you will see a couple of pieces about the lack of reproducible scientific evidence that this will occur. Lightning is such a significant event that it would be very difficult to neutralize from ground mounted systems. This is why the national Standards on lightning protection ONLY ALLOW INTERCEPTION AND CONDUCTION TO GROUND FOR SYSTEM DESIGNS. <emphasis added> <END-QUOTE>

Seems pretty clear to me that nothing has changed.


Common sense also matches this view.

How much discharge current would be required, over what period of time, to make a significant difference? Are your discharge leads glowing red hot as they madly attempt to bleed the charge off of a passing thunderhead? Has anyone measured the actual discharge current? Can we tap this energy source for the benefit of humanity?

 

[VEBill]

geekEE: "...photos of grounding on a tower antenna..."

'KGBI-FM' is, obviously, an FM station (not AM). The tower in this case is simply a really tall thing that can be, and should be, firmly grounded.

 

[rbulsara]

vebill:

This forum is no substitute for formal learning. It seems you want hear what you beleive. So you are on your own.

There is a signinficant difference in a LP system as in NFPA 780 and what you describe. What you describe a antenna on insulated bus and then with discharge air gaps is like is just a lighting arresters (surge diverters) which will only conduct and dischage to ground when sufficient voltage is built up. I am not sure this meets any standards. To me it is outright dangerous and you better not be any where near that antenna during a storm. Its like bringging high voltage line in the transmitter room.

LP system installed per NFPA 780 are intended to avoid the lightning.

 

[VEBill]

Wiki says: "[NFPA 780 standard] lightning protection system has never been scientifically or technically validated. ...No major standards body, such as the NFPA, UL, and the NLSI, has currently endorsed a device that can prevent or reduce lightning strikes. "

In other words, pseudo-science. The holistic-medicine of lighting protection. (Apologies in advance if that offends, but I call them as I see them.)

The AM antenna system that I was describing was simply a counter-example to one of your previous statements. Counter-examples are used to quickly and easily prove something is false. It only takes one counter-example to make the point. The point has been made.

 

[VEBill]

For anyone still interested, here is the link to Wiki:

http://en.wikipedia.org/wiki/Lightning_rod

Reviewing Wiki and some of the referenced articles, it's also very clear that 'the jury is still out' on the ~prevention~ of lightning.

In other words: Yet to be proven.

Just like UFOs.

 

[rbulsara]

VE1BLL:

I was just to provide you a link where airplanes and lightning was discussed. After reading your last post, I decided not to do so.

 

[VEBill]

It doesn't seem like it would be all that difficult to prove conclusively that the theory of Lightning Prevention is true.

Here is how it could be done according to The Scientific Method:

Choose a test site in a region with lots of lightning. Within that region find an installation (Army, Coast Guard) with multiple grounded towers (all similar) meeting your own carefully selected optimum mutual-distance requirements. There are probably hundreds of suitable locations in the USA and most would probably be quite supportive.

Add some tamper-proof 'strike counters' to all the similar towers. Install your Lightning Protection gadgets on half of the towers. Gather data for a year or two.

Swap the gadgets to the other towers. Gather more data for a year or two. Repeat until you've reached a minimum level of stats to prove your theory. Shouldn't take more than four years. Write a paper and get it published in a peer-reviewed journal.

If this had been done already, then there wouldn't be any controversy remaining.

Those that believe something new need to prove it. I don't mean to be difficult, but snake oil is snake oil until proven otherwise. I wouldn't be ethical to allow it to pass without comment.

PS: I work with Military Avionics. Just yesterday I was examining an aircraft Lightning Arrester and Antenna Coupler. Don't confuse P-static (discharge wicks) with lightning.