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MtnDon
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# Posted: 30 Jun 2025 09:26pm - Edited by: MtnDon
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A different topic touched briefly on lightning protection. I have had some experience with lightning, both having lightning strike damage and in setting up better protections for the next time. Member gcrank1 asked if I would share some of what I have learned. So in this topic I shall share.
Let it be known that I am not a trained and certified professional. This is based on what I have read and what I have been told in conversation with a solar electrical systems engineer.
I divide this into two pieces: One, to redirect a direct strike to earth before it can enter the structure and, two, intercepting power surges and directing them to the earth.
Before going any further, most of us probably will never have to worry about lightning. If one is concerned about lightning, the first thing they should do is invest in a proper surge suppressor system that will be connected directly to the incoming power lines. There are several brands available today. MidNite Solar brought out the first good ones about 2012. They are still among the best and can be used on or off-grid.
If you are off grid and your solar panels are maybe 25 or more feet from the home I believe installing a MidNite Solar SPD's is an absolute MUST. This is because a nearby lightning strike can easily induce a surge in the wiring between the panels and the home. An SPD configured for DC at both ends of the wiring between the panels and the house, plus an AC configured SPD at the inverter output or the service panel the inverter is connected to. As the length of the wire run from the PV array to the home increases, the chance of an induced surge increases. My 325 foot run had old style "spark jump" Delta arrestors. A couple of years after my installation, MidNite came out with their superior product. However, I never knew. It is possible the Midnite Solar SPD's could have saved the day if our strike was not a direct hit.
I'll never know. We were not present, but lightning hits were recorded in a concentrated pattern right in our area on our ridge the night we were struck. A friend in the FS showed me the online maps the FS paid to have access to. So we might have had a direct hit that would have caused damage no matter what we had done. We had one burn mark on the cabin, but that was from a string of LED lights along the eve. Was that string the cause or was it the result of lightning strinking elsewhere or inducing a surge?
I like the MidNite brand as they mount externally which makes the indicator LED easily visible. The MOV’s (Metaloxide varistor) which are the electronics devices that do the work deteriorate a little each time they interupt a surge. The blue LED indicates it is functional. I walk past mine several times in a usual day. They are are rebuildable when the LED’s no longer illuminate. I have had two rebuilt over the past 8 years or so.
For the curious the MOV works more orless like this. (this is for the DC side) One wire connects to the positive, a second wire connects to the negative and a third wire connects to the ground. The MOV has a very high resistance when the voltage is in its design range. When there is a high voltage surge, such as from a strike, the resistance istantly drops to near zero and the energy is dumped direct to the ground and the MOV resistance returns to very high.
More later as time permits. comments, questions welcome
note the led
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2 led's visible
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FishHog
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# Posted: 3 Jul 2025 07:25am
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Thanks for the MtnDon, interesting stuff and I'm doing some research on the SPD. I have 3 separate arrays, 2 roof mounted, one pole mounted about 20' away from the cottage. Its the pole mount that concerns me the most.
Is your grounding just a ground rod at the cottage, or have you also grounded your arrays? Appreciate the time you put into this. Good stuff
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Malamute
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# Posted: 3 Jul 2025 12:18pm - Edited by: Malamute
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Good information Don, thanks!
I dont have solar here, but get regular surges on the grid power. Ive thought about whole house surge protection to replace the small ones inside, but it escaped my attention until seeing your post.
I need to look into lightning protection also. I saw a strike that I thought hit the neighbors house, they were gone, i went over and watched for smoke coming out of the attic vents. Had one close strike to my place that started a fire in the sage brush, fortunately soon followed but an absolute downpour, before myself and another neighbor could get out to control it.
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MtnDon
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# Posted: 3 Jul 2025 03:28pm
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Quoting: FishHog Is your grounding just a ground rod at the cottage, or have you also grounded your arrays?
My quick answer is that in my original system there was about 300 feet between the pole mpunted array and the cabin.
Anyhow, the array was grounded directly to earth. As well, after the lightning event I installed a Midnite Solar SPD at the pole mounted combiner box and disconnect. And I installed one of the SPD's at the input side of the solar charge controller which was up the slope at the cabin.
Since the time I did my original design, the NEC has changed some of the rules regarding grounding. It also gets more complicated when we consider a lightning protection system.
I'll be back home where I can access my notes and have my computer after the weekend and maybe make some sense.
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Steve_S
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# Posted: 4 Jul 2025 01:01pm
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I've religiously used Midnite's SPD's AC & DC, seems everyone forgets the AC side of the fence but shouldn't.
Solar Array "frames & racking" are grounded to a grounding plate buried 24" deep. Rod was not practical due to rocks etc. This of course is not electrical Grounding, just the fames & racking. The DC & AC done per Midnites docs and conveniently my SCC gear is Midnite but inverter is Samlex.
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gcrank1
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# Posted: 4 Jul 2025 01:24pm
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Glad to see you still posting Steve!
Always helpful info 
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