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rockies
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# Posted: 29 Sep 2015 20:56 - Edited by: rockies
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I was waching an episode of "Cottage Life Television" and they were talking about all the ways lightning can strike a cabin. Does anyone have lightning protection?
http://www.solar-electric.com/solar-system-lightning-protection.html/
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MtnDon
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# Posted: 29 Sep 2015 22:12
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Quoting: rockies Does anyone have lightning protection?
Absolutely. Sadly it took a bad strike to make me realize what I should have done in the first place.
The cabin, small shed and large shed we call the barn all have copper air terminals. Air terminals are what are commonly called lightning rods. Ours are 5/8" copper, 18" long. The cabin has three on the peak, spaced about 15 feet apart. The chimney has its own mounted on the cap. The sheds have two each on the high side of the sloped shed style roofs. The TV antenna mast acts like an air terminal itself.
The cabin roof terminals are connected with 1/2" dia. multi strand braided wire. Special stuff for the purpose. Two down wires; one at the NW corner and the other at the SE corner. All changes of direction are gentle 12" minimum radius curves. Those down wires connect to a 5/8" x 8 foot copper clad rod driven 1 foot below surface. All fasteners are S/S or copper. Those rods are connected to a buried copper plate about 3 feet from the rod. Each corner also has a wire extending out 7 - 8 feet to a second rod. The earth has been formed to channel rain and run off water into "bowls" that permit water to soak the ground around the earthing rods and plates.
The sheds each have two rods opposite corners with extensions to a second pair of rods about 7 feet away. The TV mast is earthed to it's own rod and copper plate. Those are all interconnected into a large earthed network.
The solar array pole is earthed to three rods at 8 foot spacing as well as the steel pole itself being 6 feet in the ground and concrete mass. The earth around that was also reshaped to promote ponding and water soaking around the earthing rods.
Midnite Solar SPD's and Delta arrestors are both used in the DC section and the AC sections.
As well I have a quick disconnect cable where the PV wires go to the CC. The wires from the PV emerge from underground about 12 feet from the corner where the CC is located. They come up to a box on a post. I can throw a breaker to disconnect power and then safely unplug the wire that goes from the pole mounted box to the CC. That gives me a gap that hopefully lightning will never jump in the event of a direct strike on the PV array. Of course that is only good if I am there to disconnect. During out lightning season I often disconnect that when we leave for periods of up to 10 days or so. Fortunately with all loads turned off the batteries manage quite well if left in a full SOC before we depart.
The lightning strike knocked out virtually everything with solid state parts, blew ends of the Delta arrestors we had and split a HD DC breaker in half. Lots of fun stuff.
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MtnDon
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# Posted: 29 Sep 2015 22:13 - Edited by: MtnDon
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If you look at the map in that link that was posted we are in the second worst area in the northern part of NM.
We were very happy we were absent when the strike occurred. We believe there were more than one actual strike within 20 feet of the cabin. As well as the electronics damage there are electrical scorch marks on part of a gable end and one eve. A joiner when 2 sections of aluminum gutter were couple was blow apart.
The generator in the barn had been left with the cord plugged in. Lightning energy backed through the system and blew out the inverter box. I now never leave the generator with any cords plugged into it.
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Martian
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# Posted: 30 Sep 2015 07:09
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I find it difficult to believe that we can control the flow of voltage contained in a lightening strike with a wire of ANY size. After all, it just jumped across miles of open sky. Has anyone had a strike on a "protected" structure that didn't sustain any damage?
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MtnDon
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# Posted: 30 Sep 2015 09:48 - Edited by: MtnDon
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I have a friend in the forest service who has been on lookout duty in the local tower during many thunder and lightning storms. He says you sit there on the wood stool with glass insulators on the leg ends and watch the light show. They are basically inside a well grounded cage with glass windows all around. The storm rages, lightning flashes and their lights, radio equipment, refrigerator, computer, etc. continue to function.
What I have is something similar. I hope to keep the induced lightning energy outside of the cabin system. The SPD's will hopefully divert any induced energy. If a direct strike happens we hope it follows the easiest path to ground, electricity is after all supposed to take the path of least resistance. That what we have tried to provide. Yes lightning does travel huge distances through air. It does all sorts of things like jumping sideways through trees and branches also.
I feel better having done something more than hoping it'll happen to the other guy rather than me. What we've installed won't hurt us, but may help prevent buying another round of new equipment. However if a direct strike gets inside either the building or the wiring all bets are off.
Oh, and cell phone towers have similar earthing setups and survive lightning all the time. Ditto TV and radio.
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leonk
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# Posted: 30 Sep 2015 11:31
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mntdon, interesting about the tower.
I was always wondering why houses around here don't have any ligthing protection (Ontario), farms usually do. Where I come from in the old world it was very common.
It's not as critical I guess in the woods, where most trees are higher than the house. Installing TV antenna I knew proper grounding is critical.
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bldginsp
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# Posted: 30 Sep 2015 11:44
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We had a house in our city that had a properly grounded electrical system, and was hit by lightning with disastrous effects. Switches and receptacles exploded, tile on shower walls exploded off as the wire lathe conducted electricity and vaporized the moisture in the tile mortar instantaneously. A properly grounded electrical system is supposed to guard against lightning but is a far cry from a proper lightning rod system such as Don installed.
One thing to remember about lightning is that even though it has millions of volts the amperage is relatively low so you are not dealing with millions of watts. So anyway the wire sizes don't have to be astronomical to be effective. The most important thing seems to be their location and the design of the overall system, such as Don researched and implemented.
One thing I'm worried about is putting copper up on a roof with galvanized roofing. Just the water dripping off of copper onto galvanized iron can be enough to set off a galvanic reaction, so I hear. I'm going to look into aluminum for that reason.
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MtnDon
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# Posted: 30 Sep 2015 14:13 - Edited by: MtnDon
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Quoting: leonk where most trees are higher than the house.
That was what I used to think. Before we were struck. Surrounded by trees that are 50 - 70 feet taller than the cabin. Three trees about 20+ feet from the cabin were also hit. Maybe it jumped sideways. Maybe there were multiple hits.
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rockies
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# Posted: 30 Sep 2015 18:00
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I think a lot of people living in the country forget about how many different ways lightning can enter the cabin. It can hit the building itself, your solar panels, your water tower, even come down a phone landline. One thing I've seen mentioned on shows about lightning protection is to have a whole house surge protector installed on your electrical panel, and then use separate surge protectors for electronics and appliances. Lots of people plan for fire safety, but not many think about lightning protection.
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