Lightning Protection Requirements

[philly]

I don't have much experience with lighting protection but have a customer requesting lighting protection on outdoor switchgear and a new building/structure.

Has anyone provided specific lighting protection for outdoor switchgear and if so what does that look like? I always thought that you simply ground the enclosure with a ground ring or similar and that would take care of the requirement? Are there any calculations, special requirements etc.. for providing this protection?

With buildings I know this may be more straight forward? Is there a particular requirement in the NEC for this or is this usually customer preference? Again are there any specific calculations, design procedures, etc... for providing this protection?

 

[petersonra]

I don't have much experience with lighting protection but have a customer requesting lighting protection on outdoor switchgear and a new building/structure.

Has anyone provided specific lighting protection for outdoor switchgear and if so what does that look like? I always thought that you simply ground the enclosure with a ground ring or similar and that would take care of the requirement? Are there any calculations, special requirements etc.. for providing this protection?

With buildings I know this may be more straight forward? Is there a particular requirement in the NEC for this or is this usually customer preference? Again are there any specific calculations, design procedures, etc... for providing this protection?

Lightning protection systems are somewhat complex and generally don't work as well as one would hope.

They are designed by UL listed lightning protection designers, installed by UL listed lightning protection contractors, and than inspected by UL after the installation is complete.

There is no NEC requirement to provide a LPS. It may be required by other codes in certain cases.

 

[steve66]

Lightning protection systems are somewhat complex and generally don't work as well as one would hope.

They are designed by UL listed lightning protection designers, installed by UL listed lightning protection contractors, and than inspected by UL after the installation is complete.

There is no NEC requirement to provide a LPS. It may be required by other codes in certain cases.

Around here, if an LPS system is installed, there is no requirement to have it designed by a UL designer, no requirement to have it installed by a UL listed contractor, and no requirement to have UL list it.

At least around here, if Joe Blow wants an LPS, he is free to install whatever and however he wants, as long as its tied back to the building ground. Sure, it may not meet any standard, but its probably still better than nothin.

 

[petersonra]

Around here, if an LPS system is installed, there is no requirement to have it designed by a UL designer, no requirement to have it installed by a UL listed contractor, and no requirement to have UL list it.

At least around here, if Joe Blow wants an LPS, he is free to install whatever and however he wants, as long as its tied back to the building ground. Sure, it may not meet any standard, but its probably still better than nothin.

That's a good point. you can add whatever amount of grounding you want. It won't do any good but you can add it.

If you are required to have a LPS, it generally has to be listed. I don't know what the requirements are for a non-required LPS. I think if you call it a LPS, it probably needs to be an actual LPS and not just some extra grounding electrodes that serve no real purpose.

How would a building department be able to evaluate a LPS if it is not listed? If you claim you are installing a LPS on your plans that are submitted to the building department, it probably needs to be an actual LPS and not some home brew scheme of dubious utility.

 

[Bugman1400]

The typical lightning protection for a substation may be a similar application to what you're looking for. Basically, a sacrificial conductor is used to draw the strike to ground. On transmission lines and substations, a static wire is used. In theory, the static wire is typically strung well above and acts as an umbrella to shade the protected equipment below from direct hits. The higher the static wire, the larger the shade of protection of the equipment below. However, at some height, the protection starts to fade since a strike could occur from the side instead of from above. Lightning rods mounted at the highest point on a building act the same way but, typically more are used because the shading effect of the umbrella is less because the height of the lightning rod is less.

 

[junkhound]

Awhile back saw a few buildings in FL with a chain link fence over and around the HVAC equipment on the roof. Made query to an engineer about how effective is that for lightning, which is why I assumed the fence was installed on the roof (4 story building).


Nah, says he, the fence is to slow down the druggies trying to strip and steal the copper!!! hmy:


If a meter or so away from equipment, think the fence would be good lightning protection also.

 

[petersonra]

Awhile back saw a few buildings in FL with a chain link fence over and around the HVAC equipment on the roof. Made query to an engineer about how effective is that for lightning, which is why I assumed the fence was installed on the roof (4 story building).


Nah, says he, the fence is to slow down the druggies trying to strip and steal the copper!!! hmy:


If a meter or so away from equipment, think the fence would be good lightning protection also.

Now that I think of it, I have seen a few similar installations where chain link fence is installed around and on top of outdoor equipment. I always figured they were worried about kids climbing in there and getting hurt. I bet it was really about thieves.

 

[Strathead]

I don't have much experience with lighting protection but have a customer requesting lighting protection on outdoor switchgear and a new building/structure.

Has anyone provided specific lighting protection for outdoor switchgear and if so what does that look like? I always thought that you simply ground the enclosure with a ground ring or similar and that would take care of the requirement? Are there any calculations, special requirements etc.. for providing this protection?

With buildings I know this may be more straight forward? Is there a particular requirement in the NEC for this or is this usually customer preference? Again are there any specific calculations, design procedures, etc... for providing this protection?

NFPA 780 covers Lightning protection standards. And as mentioned UL has lightning standards. They are occasionally in conflict from what I understand. I don't have a lot of understanding, but I do grasp some of the basic concepts and installation requirements. I wouldn't do the install myself. I call one of three or four who install per UL in my area, and let the deal with it.

 

[ggunn]

The typical lightning protection for a substation may be a similar application to what you're looking for. Basically, a sacrificial conductor is used to draw the strike to ground.

I am not an expert on lightning protection, but the reading I have done has said that the way lightning rods work isn't to draw a strike to ground. They present the ground potential up above the structure they are protecting and their tips are made very sharp so that the planes of equal potential are squeezed very close together as they traverse the pointed end of the rod when a significant charge is nearby. If the charge is more than a certain magnitude the charge gradient exceeds the ability of the air to act as an insulator and the differential charge is dissipated gradually before a strike can occur. This dissipation (and I'm just repeating what I have read) is sometimes apparent as a visible glow around the tip of the rod and is responsible for what is known as St. Elmo's Fire.

This makes sense to me because from what I have read about the magnitude of current that flows in a lightning strike, it seems to me that it would greatly exceed the current carrying ability of the conductors I have seen connected to lightning rods if a rod were to attract a strike.

 

[brantmacga]

Around here, if an LPS system is installed, there is no requirement to have it designed by a UL designer, no requirement to have it installed by a UL listed contractor, and no requirement to have UL list it.

Engineers typically ask for UL master label though; doesn't seem to be the case here but every job I've done that had it spec'd, that is the requirement.



Sent from my iPhone using Tapatalk

 

[publicgood]

Lightning Protection Requirements

You would provide air terminals on all (4) corners. Then additional terminals at intervals not to exceed (20) feet. All air terminals are at least (10") tall and tied together with UL listed Type 1 or 2, depending on height, cable. Additional air terminals are placed if the protected structure has roof with distances greater than (50) feet for flat roofs. A minimum of (2) downleads are provided - placed at opposite ends and again every (100) feet, although likely not that long in this case. These typically connect to a ground ring: minimum #2 by NEC. The ground ring connects ground rods, bonds to the structure and also the the grounding electrode system. It can be other than a ground ring, but this is most effective and typical.

 

[publicgood]

Lightning Protection Requirements

Around here, if an LPS system is installed, there is no requirement to have it designed by a UL designer, no requirement to have it installed by a UL listed contractor, and no requirement to have UL list it.

At least around here, if Joe Blow wants an LPS, he is free to install whatever and however he wants, as long as its tied back to the building ground. Sure, it may not meet any standard, but its probably still better than nothin.

Agree. It does have to be listed materials, but it doesn't have to be a listed design. Other than UL it could be a LPI listed design. What I have found: if you go through the cost to design it to a listing, depending on the scope of the project, the additional cost to have it listed is only $2-3k.

One might look to their insurance carrier requirements also.

You'll need to cover all details for a complete listing, such as listed surge protective devices.

 

[kwired]

Now that I think of it, I have seen a few similar installations where chain link fence is installed around and on top of outdoor equipment. I always figured they were worried about kids climbing in there and getting hurt. I bet it was really about thieves.

If they are going to climb several stories first I don't think a chain link fence is going to deter them once they get there.

I thought of it possibly being a barrier so fall protection isn't required for anyone working on the equipment inside the fence.

 

[philly]

You would provide air terminals on all (4) corners. Then additional terminals at intervals not to exceed (20) feet. All air terminals are at least (10") tall and tied together with UL listed Type 1 or 2, depending on height, cable. Additional air terminals are placed if the protected structure has roof with distances greater than (50) feet for flat roofs. A minimum of (2) downleads are provided - placed at opposite ends and again every (100) feet, although likely not that long in this case. These typically connect to a ground ring: minimum #2 by NEC. The ground ring connects ground rods, bonds to the structure and also the the grounding electrode system. It can be other than a ground ring, but this is most effective and typical.

This sounds like an effective means for providing protection for a building or structure. But what about equipment located outdoors. For example several pieces of outdoor rated switchgear that may be sitting on a concrete pad? Does this equipment typically require such protection even if being requested by the customer?

 

[Sahib]

what about equipment located outdoors. For example several pieces of outdoor rated switchgear that may be sitting on a concrete pad? Does this equipment typically require such protection even if being requested by the customer?

Individual lightning masts mounted near/ on switchgears may be provided with suitable protection angle.

 

[publicgood]

Individual lightning masts mounted near/ on switchgears may be provided with suitable protection angle.

Agree - there may be surrounding protection. NFPA 780 even has trees as a possible means that should be reviewed and connected the the lightning protection system.

This sounds like an effective means for providing protection for a building or structure. But what about equipment located outdoors. For example several pieces of outdoor rated switchgear that may be sitting on a concrete pad? Does this equipment typically require such protection even if being requested by the customer?

See 780 Annex L for a risk assessment.

For say roof top mechanical equipment, you would be putting air terminals on top of this equipment; so yes, if your gear is not protected and it is an owner requirement to have it protected...this is the same approach we would take.

I've seen this mostly for walk-in switchgear. Non-walk-in switchgear is typically closer to the building and within the available zone of protection already.

 

[Sahib]

Of course, there would be bypasses: low intensity lightning attaching to switch gears instead of to lightning conductors. SPD's might help in such cases also.

 

[Bugman1400]

I am not an expert on lightning protection, but the reading I have done has said that the way lightning rods work isn't to draw a strike to ground. They present the ground potential up above the structure they are protecting and their tips are made very sharp so that the planes of equal potential are squeezed very close together as they traverse the pointed end of the rod when a significant charge is nearby. If the charge is more than a certain magnitude the charge gradient exceeds the ability of the air to act as an insulator and the differential charge is dissipated gradually before a strike can occur. This dissipation (and I'm just repeating what I have read) is sometimes apparent as a visible glow around the tip of the rod and is responsible for what is known as St. Elmo's Fire.

This makes sense to me because from what I have read about the magnitude of current that flows in a lightning strike, it seems to me that it would greatly exceed the current carrying ability of the conductors I have seen connected to lightning rods if a rod were to attract a strike.

Very well put and is the way I understand it also. It is also an interesting fact that a lightning strike is actually made up of multiple strikes. If you slow down a film of a strike you can see the light pulsating several times.