When do you need a Lightning Protection System?

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jtinge

jtinge

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Hampton, VA
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Sr. Elec. Engr
I realize there is no NEC requirement, other than 675.15 Lightning Protection, to have a Lighting Protection System, only what to do with it if you have one.

NFPA 780 addresses the installation of LPS's but states in Annex L.1.1.2-When required, a lightning protection system should be installed in accordance with the requirements contained in this standard.

So I'm interested in what factors or criteria you use to determine whether you need an LPS or not.
 
Strictly speaking, a lightning protection system is never required by any NFPA document. However, insurance companies might have a say in the matter. But it is essentially an owner?s call. NFPA 480 gives a process for assisting in the design decision. The factors that go into the process include,

  • The geometry of the building (i.e., how tall is it, how spread out is it),
  • The materials of construction (i.e., how susceptible to fire is that material)
  • The proximity of nearby tall buildings and tall trees,
  • How much of a disaster would there be if the building burned down (i.e., is this a storage warehouse for old furniture or is it an elementary school),
  • How often lightning strikes the geographic area in which the building is constructed (there is a map of the world that has the answer to this question),

When all factors are put into their respective equations, you end up with two numbers that essentially speak to the probability of a lightning strike event and the consequences of such an event. If one of the numbers is larger than the other, the NFPA design process gives you the result that a lightning protection system is recommended (note: not ?required,? but only ?recommended?). If the other number is the larger of the two, then the result is that a lightning protection system is not warranted.

 
jtinge said:
I realize there is no NEC requirement, other than 675.15 Lightning Protection, to have a Lighting Protection System, only what to do with it if you have one.

NFPA 780 addresses the installation of LPS's but states in Annex L.1.1.2-When required, a lightning protection system should be installed in accordance with the requirements contained in this standard.

So I'm interested in what factors or criteria you use to determine whether you need an LPS or not.
Click to expand...

If the jurisdiction has adopted NFPA 780 then it's required, in my opinion. Back when we used to adopt specific NFPA standards we referred to them in ordinance by "pamphlet number". I'm not sure what your jurisdiction is doing these days but you can either research it or make some phone calls. Agencies to call would be local fire marshal, state fire marshal, local building department. And all that depends on who has jurisdiction on your project. If you're doing federal, military, some educational, etc. they may be regulated by other entities or self-regulated.

To answer the question posed in the title of your thread, that answer is "Before you get hit by lightning!" (sorry, had to do that)
 
We have LPS here at a nearby submarine base where nuclear weapons (Trident D-5's) may or may not be stored. There are two fences around the weapons facility and marines with automatic weapons patrol this area between the fences.

So an LPS is based on what you are protecting. I saw a LPS on a historic tree in New Orleans.
 
mgookin said:
If the jurisdiction has adopted NFPA 780 then it's required, in my opinion. Back when we used to adopt specific NFPA standards we referred to them in ordinance by "pamphlet number". I'm not sure what your jurisdiction is doing these days but you can either research it or make some phone calls. Agencies to call would be local fire marshal, state fire marshal, local building department. And all that depends on who has jurisdiction on your project. If you're doing federal, military, some educational, etc. they may be regulated by other entities or self-regulated.

To answer the question posed in the title of your thread, that answer is "Before you get hit by lightning!" (sorry, had to do that)
Click to expand...

I don't agree. If a jurisdiction has adopted NFPA780 then all that means is that if something is actually required by NFPA780 than you have to do it like NFPA780 says you have to do it IF you do it. But, if NFPA780 does not require it, it is not required.

Look at it this way, if the NEC is adopted, that does not mean you are required to have class 2 circuits in every house just because article 725 is part of the NEC.
 
You should perform a risk assessment in accordance with Appendix L, and use that.
 
petersonra said:
I don't agree. If a jurisdiction has adopted NFPA780 then all that means is that if something is actually required by NFPA780 than you have to do it like NFPA780 says you have to do it IF you do it. But, if NFPA780 does not require it, it is not required.

Look at it this way, if the NEC is adopted, that does not mean you are required to have class 2 circuits in every house just because article 725 is part of the NEC.
Click to expand...

Kind of like the ole "data room" in the NEC? Nothing says you have to have one, but if you declare one, this is how you shall build it.

I'll buy that.
 
Lighting Protection

Lighting Protection

tom baker said:
We have LPS here at a nearby submarine base where nuclear weapons (Trident D-5's) may or may not be stored. There are two fences around the weapons facility and marines with automatic weapons patrol this area between the fences.

So an LPS is based on what you are protecting. I saw a LPS on a historic tree in New Orleans.
Click to expand...

The federal government has very strict guide lines when dealing with lightning protection, depending on location, just drove 10' by 3/4" copper clad ground rods, 0-10 ohm resistance requirement, this was at a explosive demolition site.
 
mgookin said:
Kind of like the ole "data room" in the NEC? Nothing says you have to have one, but if you declare one, this is how you shall build it.

I'll buy that.
Click to expand...
Actually you can declare it and still wire it the ordinary way and not have to meet the specific restrictions. Or you can declare it and choose to take advantage of the special provisions AS LONG AS you meet all of the requirements.
 
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