Lightning protection system

[sw_ross]

I live in farm and ranch country, North Dakota. A lot of the old ranch and farmsteads have lightning protection systems installed that are probably original to the home which was probably built in the 40's and 50's.
They all have the aerials and lines going to ground. Most of the homes are the tallest thing for miles around.

You don't see them on rural homes that were built more recent than about the 70's (that I'm aware of).

Recently I looked at plans for an engineered federal job that was spec's out with an involved lightning system. I don't have any experience with these systems and it looked very involved (more so than just a few aerials and copper wire).

What are the thoughts about whether they are justified? Why don't you see them installed on newer homes? Especially in place like Florida?

 

[sw_ross]

Has anyone been involved in this type of installation? Or is it just hype?
when I google it I mostly get companies that are marketing their products.

 

[hbiss]

Recently I looked at plans for an engineered federal job that was spec's out with an involved lightning system. I don't have any experience with these systems and it looked very involved (more so than just a few aerials and copper wire).

Because it's a federal job should answer that question.

What are the thoughts about whether they are justified? Why don't you see them installed on newer homes? Especially in place like Florida?

As for not seeing them on newer homes, that's probably because nobody says they have to have them and they cost money. Betcha the lightning protection on those old places was done by the farmers with material bought from the farm stores. Probably had lots of experience doing silos and such.

-Hal

 

[hbiss]

Has anyone been involved in this type of installation? Or is it just hype?
when I google it I mostly get companies that are marketing their products.

Definitely not hype. There are lots of buildings and structures that require lightning protection. Don't know if there is anybody here that does that kind of work, it really has nothing to do with electrical contracting. You have to have training and a certification to install lightning protection systems much like we have to be licensed to do our work.

-Hal

 

[sw_ross]

Definitely not hype. There are lots of buildings and structures that require lightning protection. Don't know if there is anybody here that does that kind of work, it really has nothing to do with electrical contracting. You have to have training and a certification to install lightning protection systems much like we have to be licensed to do our work.

-Hal

So if a project, like the one I was describing, has a lightning protection system spec'd out on the electrical drawings page it has to be done by a certified person/company? Basically, has to be sub' out, like a fire alarm system, etc?

 

[hbiss]

Yup.

-Hal

 

[paulengr]

Definitely not hype. There are lots of buildings and structures that require lightning protection. Don't know if there is anybody here that does that kind of work, it really has nothing to do with electrical contracting. You have to have training and a certification to install lightning protection systems much like we have to be licensed to do our work.

-Hal

There is no certification. I do inspections on these.

Lightning protection is really straight forward. First part is grounding the structure properly, plus lightning rods, static lines, etc. There is a bunch of “dissipator” or “eliminator” products that are pure snake oil. Then it’s just a matter of protecting the electrical equipment as lines pass in and out of the protected structures. First calculate the average strikes per year (based on location and area). Then insulation coordination which determines what percentage will do damage. This looks at your BILs and line lengths since the farther you are from a surge arrester (in feet) the less protection it offers. Then add surge arresters as needed to decrease the possibility of a damaging strike to an acceptable level.

NFPA 780 and.a couple IEEE standards explain this but it’s still almost Ben Franklin technology. Due to EMTP we are learning some things don’t actually work as expected like whole house lightning arresters.

There will always be lightning that simply can’t be stopped. There is a Duke 230 kV transmission line about 25 miles from my house that took a hit so big in hurricane Irene that it blew the support structure in half. This is Duke, not some little co op, built to withstand 120+ MPH winds, and a transmission line, not a grade B residential line. BIL was around 2 million Volts. As I said...you can’t stop lightning, just reduce the chances of a hit. Even if you have perfect lightning protection you can get a back flash where it hits the ground nearby then the ground potential rise flashes over without a direct strike.

 

[texie]

Has anyone been involved in this type of installation? Or is it just hype?
when I google it I mostly get companies that are marketing their products.

In my experience lightning protection systems are usually subbed out to a UL Certified lightning contractor. Often the job specs and/or the AHJ require UL certified contractors. Even if UL certification is not required this is the kind of work that unless you do it regularly it us usually more economical to sub it out.

 

[hbiss]

There is no certification. I do inspections on these.

In my experience lightning protection systems are usually subbed out to a UL Certified lightning contractor. Often the job specs and/or the AHJ require UL certified contractor

This has been my experience also. I believe the insurance carrier has something to say about it too.

-Hal

 

[kwired]

probably a big risk to be an installer as well, and because of that probably not cheap to have installs done. All you are doing is minimizing the damage potential, you can't really control if there ever will be a hit or not.

 

[brantmacga]

In my experience lightning protection systems are usually subbed out to a UL Certified lightning contractor. Often the job specs and/or the AHJ require UL certified contractors. Even if UL certification is not required this is the kind of work that unless you do it regularly it us usually more economical to sub it out.

Same here....

Also, I’ve done some state and federal jobs, and the local AHJ’s do not have jurisdiction over the projects I’ve done. On the federal job inspections were done by a UL inspector. On state jobs, it was a state facilities employee.


Sent from my iPhone using Tapatalk

 

[ron]

The systems are an optional insurance policy that most folks don't take.
When we design them, we specify compliance with UL 96A and the installer is listed by UL ul.com/lightning at that they provide a Master Label

 

[PaulMmn]

Back in NJ our Scout camp had lightning rods and grounding wires. It was half-way up a mountain (well, it was NJ, so it was more like a hill), surrounded by trees taller than the lightning rods. In the 20 years I was active, it was never hit by lightning. But that's one of those negative proofs.

Belt + suspenders is better than nothing. If your pants don't fall down, which one saved them?

 

[Sfg9972]

There are many guidelines and codes as mentioned before. NFPA 780 , UL 96, LPI 155 that would help you install yourself. Lightning rod, conductor, proper metallic body bonding and grounding is basically it. Use required UL listed parts, place ground rods appropriately, follow down conductor routing requirements, and correct amount of ground rods for size and configuration of the structure. Yes, you probably would come out cheaper generally speaking what your time is worth if you went with Master Label installers plus rest assured it was done by professional. Best of luck

 

[ggunn]

Back in NJ our Scout camp had lightning rods and grounding wires. It was half-way up a mountain (well, it was NJ, so it was more like a hill), surrounded by trees taller than the lightning rods. In the 20 years I was active, it was never hit by lightning. But that's one of those negative proofs.

Belt + suspenders is better than nothing. If your pants don't fall down, which one saved them?

Lightning rods don't "attract" lightning; they dissipate the charge differential between ground and sky so that strikes are less likely to happen.

 

[don_resqcapt19]

We did one when the lightning sub-contractor backed out. The company that supplied the lightning protection equipment gave us all of the information we needed and arranged for the UL Certification so we could get the required UL Master Label. It was not a big deal.

Harger makes and sells the required parts, will provide you with a detailed design, and even runs a free class on the installation of lighting protection systems.

 

[junkhound]

Lightning rods don't "attract" lightning; they dissipate the charge differential between ground and sky so that strikes are less likely to happen.

You actually believe that? (See paulengr previous post on snake oil.)

Versus providing a preferred path to ground that does not result in structure damage or fire?

 

[ggunn]

You actually believe that? (See paulengr previous post on snake oil.)

Versus providing a preferred path to ground that does not result in structure damage or fire?

Yes, I do. The typical lightning strike contains far more current than be safely carried to ground by the #6 (or whatever) grounding conductors that lightning rods are wired with.

 

[junkhound]

Seems to be a common misconception.
Late 60's and early 70s was when the 'lightning prevention dissipator' snake oil folks started making their pitches, perhaps pauleng can add his knowledge on the 'snake oil' aspect of dissipation.

Typical lightning is 20 kA 1/e duration of 30 us. That is an I^2*t of 12,000 Asg-sec.

Largest lightning stroke ever recorded is 3 megamps, which would leave 6 AWG in little short pieces.

6 AWG can carry 100,000 amp lightning pulse (only 1% probability of strike that large). Granted, if wire has just 90 C insulation, the insulation will be bubbled or gone.
Note that the 30us is fast enough that skin effect is a factor, thus 3/8" or 1/2" type L or K copper tubing is a much better grounding conductor for lightning than electrical wire.

Simplistically, using your 6 AWG and looking at 100A fuse curves to simplify the I^2*t comparisons, typical I^2* fuse rating is 47,000; thus, 6 AWG easily capable of carrying a normal lightning stroke current. Copper cable or tubing fusing is much higher than fuse material.

Over the last 50 years, have run thousands of high current lightning and EMP pulse tests up to 4 megamps on up to 250MCM cables. One of the reasons, other than inductance, for keeping the ground runs straight is magnetic forces. Note that a 4 megamps pulse will not fuse 250 MCM, but if there is a 1 ft radius 90 deg bend the magnetic forces will BREAK 250 MCM as the tons of force try to make the curve into a straight wire. Have some 10000 frame/second videos (cannot share, company proprietary) showing a curves wire magnetic forces trying to expand the radius and breaking the wire or breaking the terminations.

 

[synchro]

One of the reasons, other than inductance, for keeping the ground runs straight is magnetic forces. Note that a 4 megamps pulse will not fuse 250 MCM, but if there is a 1 ft radius 90 deg bend the magnetic forces will BREAK 250 MCM as the tons of force try to make the curve into a straight wire.

A similar effect is the "pinch" magnetic force that can crush a tubular conductor if the currents are high enough. I've seen pictures of a copper downspout that was crushed by a lighting discharge.
The pinch effect is also used for confining plasma in nuclear fusion experiments, although instabilities can make this difficult.

Ampère's force law - Wikipedia

en.wikipedia.org

Z-pinch - Wikipedia

en.wikipedia.org