RE: lightning rods

Organic Farmer · November 2013

I am nearing completion of mounting my solar panels onto their mounting structure. This structure is 70' long and 8' high. I had gotten it all up once, a year-ago, one week before Sandy blew through and took it all down. Now after a re-design here I am again.

I am installing two lightning rods. One on either side of the array; one near the West end; the second near the East end; but on opposite sides of the array.

I had a long conversation with two electrical contractors, and they were clearly uneducated on the mechanics of lightning rods. They knew a great deal about grounding though. The entire structure is well grounded 10X over.

Each 'lightning rod' I am installing is basically as follows.

A 8' long 5/8" copper-coated rod pounded in the ground with 6" showing. A 6' steel T-post to act as a support. With a 8' conduit pipe U-bolted to it. Then a second 8' long 5/8" copper-coated rod U-bolted to the conduit pipe. Then a length of 6-gauge copper clamped to both copper rods [one in the ground, the second in the air].
The upper rod will reach about 19' above grade.

The top of the array's structure is 8' high, so these lightning rods will reach >10' above that, and their zone of protection should basically straddle the array.

Now I understand that there is debate, whether rods protect from strikes that would have happened anyway. Or if they tend to act more to attract strikes. But in either case, well placed rods should serve to prevent structures under them from being struck.

What is your learned opinion?

mike95490 · November 2013

Re: lightning rods

Organic Farmer wrote: »

... well placed rods should serve to prevent structures under them from being struck.
...What is your learned opinion?

"should " being the important word here. The EMP/induced currents, from a near strike to the rods, is likely to fry a lot of stuff unless you have both Deltas and Midnight protectors.

niel · November 2013

Re: lightning rods

i'm confused why the 2nd rod attachment in that manner? heck 1/2 of a piece of standard 1/2 inch pipe could've been attached or even use pvc pipe and run several copper wires spaced out and up it secured with hose clamps. at the top the wires could spike outward several inches on all sides allowing greater effective area. nearly anything could work if it can carry heavy currents.

Organic Farmer · November 2013

Re: lightning rods

Copper rod appears to be the most common device for attracting strikes. Barns in this area often have them.

One friend recently saw his solar-array struck by lightning, his inverter/charge-controller was fried, and some of his wiring melted.

Another friend's home was struck this summer, they lost much of their home wiring.

I understand that any wire could serve the purpose [until it vaporizes]. Whatever is going to take the full strikes needs to be of sufficient size and capacity that it does not melt or vaporize, and that it can take repeat strikes.

I have made an assortment of homestead things with PVC [chicken-tractors, portable fencing panels, etc]. I have found that PVC becomes brittle and weak quickly when exposed to sunlight year-round.

niel · November 2013

Re: lightning rods

yes, i suppose it could be a better material than pvc, but that only gets brittle due to uv light and would need painted. the multiple wires would add to be a larger gauge and no wire would be vapor proof from a strike and even your rod could be destroyed from a strike. my point was it does not have to be more of the ground rod sticking up in the air.

not sure i'd want conduit in contact with it either as dissimilar metals react with one another. other than that it'll work as a lightning rod. keep in mind most rods are only copper plated for strength when pounding them into the ground and to make them cheaper.

a cheap option may be to use fencing poles and just run a heavy gauge jumper from that to the rod. be sure to use stainless steel clamps on the pole and snip a tad of the excess off of the end to place between the wire and the pole to prevent corrosion.

hemmjo · November 2013

Re: lightning rods

From my limited understanding of lightening protection, a properly designed system is constantly feeding small electrical charges to ground to keep a major strike from happening. I have read a bit about the various school of thought in regard to lightening protection systems. This is the only explanation that makes sense to me.

If you think about, it we talk about the size of conductors to carry the tiny (in comparison to lightening) loads we deal with. I doubt if any of us could afford the conductors required to channel a direct lighting strike to ground without vaporizing. Millions of volts at 100's of thousands of amps would require huge conductors, even if the surge is only a fraction of a second, matching huge insulated mounts and similarly huge ground rod arrays.

my 2 cents,

John

BB. · November 2013

Re: lightning rods

I don't live in lightning prone areas--so take my thoughts with a grain of salt... We had similar discussions before I and I am not sure that you can "bleed" current from a storm in any meaningful amount.

Rather than repeating, here is a good thread where we discussed some of these issues:

Off grid grounding technique?

The variable nature of lightning--One method is to use a 60 meter (~200 foot) radius "rolling ball"... Anything that contacts that sphere is in the target range of a single strike. Being on a 200' tower vs being on the ground ~200' away is about the same change of a strike.

My belief is that you want dedicated lightning "antenna" and heavy cabling to intercept the strike and move the current away from critical circuits/people/etc. You have a 200' metal radio tower... You ground it (to move current away from attached building)--The tower is at a "near ground" potential and a great lighting attractor. You "float" the tower, and you can have thousands of volts of static electricity (~100 volts per meter earth's natural E field--much much more under a thunder storm)--And you have risks of static discharge/lightning energy energizing the tower--And your radio gear in the building.

-Bill

Organic Farmer · November 2013

Re: lightning rods

That is a great thread. Thank you for showing me.

My house is a faraday cage [with exception of our windows]. I live in an area where lightning is not unusual, and we know people who have recently seen their homes / PV arrays damaged by lightning.

I did 20+ years on submarines. On-base near the piers are always power-poles at about 40-foot distances, all with lightning rods on them. Which then allowed us to transport and work on sensitive equipment on the piers and topside on the boats. From that experience, I have taken the attitude that if strikes are going to happen, I want them to happen on my terms. Where I design for them to happen. Obviously to take dozens of strikes every year, for decades, the rod and wiring needs to be fairly sturdy.

niel · November 2013

Re: lightning rods

in regards to john's comments, static dissipation does work to a degree for bleeding off even a tad of it will make it less of a target because surrounding objects further out still have the full charge and thus the full attraction. this isn't something i'd bank on though. in the event of a full blown strike the lightning rods will direct the energy to ground even if it does blow the rod or wires apart from the strike. that will be hot flying shrapnel at that point so a tad of distance from the pvs and house is a good idea. it doesn't have to be too far, but far enough the metal cools a bit and loses some of its momentum. this does not have to be the tallest object around either, but just taller than the items to be protected.

mike is right that the emp from the strike will damage your equipment so the spds are a good idea. a high discharge into the spds will cause the movs inside to explode so keep that in mind when mounting them. with this much energy there are no guarantees your equipment will survive as enough energy can be there prior to the movs tripping and clamping down on it. of course you've heard me say there aren't any guarantees when it comes to lightning, only increasing your odds.

RE: lightning rods

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