SPD placement?

arby · March 2015

Hello,
I am confused as to the number , type and placement of Surge protectors on my off grid system.
Thanks for any advice,
RB

mike95490 · March 2015

Your system engineer will be able to help you. The input of the Charge Controller, and both inputs and outputs of the Inverter

arby · March 2015

Thanks, but I am, along with this forum, and a lot of trial and error, my system engineer.
So, I don't need one on the combiner box on the pole mounted panels? they are 50 meters from the controller. Also I thought that one was needed on the breaker panel in the cottage.

BB. · March 2015

You want the Surge Protectors to reduce the chances of lighting energy getting into your system.

One at the Solar Array Fuse/Breaker combiner box. A second where the DC power enters the cabin (assuming 3-10 meters or longer cable run from array to cabin).

And, interestingly, one of the folks from NAWS years ago said lots (most?) of their lighting damaged equipment was the AC output of the AC inverters--So placing a surge suppressor at the inverter output/main AC panel).

So, if cost is an issue, one at the AC inverter/main panel. Second would be DC entrance to building. Third would be at the Solar Array Combiner. In my humble opinion.

-Bill

BB. · March 2015

I should add that, as mentioned by others here in other threads, if you a good chance of direct strikes--Using Lighting Rods (Antennas/Air Terminals) placed above / behind the panels will help a lot too.

You don't want the lighting to hit your system/wiring in the first place. And a direct strike is probably going to toast the system no matter what protection you have.

-Bill

CALLD · March 2015

If it's lighting you are concerned about then as Bill said "you don't want it to hit your system in the first place"

But lightning is a very unpredictable creature, I've seen it strike in the strangest of places and the "Highest and most conductive object' rule of thumb is often ignored by lighting. In lighting prone areas around the world measures taken to protect property are often quite extensive and involve metal poles 3 times the height or more placed about 30ft away from the property and grounded using several hundred feet of conductors underground spreading out like tree roots. The reason for the lighting rod being at least 30ft from the property is to try and reduce the effect of the magnetic inductance pulse(s) that can induce dangerous surges in nearby wiring not even electrically connected in any way.

Sometimes the best thing you can do is what insurance companies do - calculate your odds of getting hit where you are and work out if trying to protect your equipment from a hit is cheaper or more expensive than replacing it in the event of a hit.

In my case the odds of getting hit were too low to justify doing anything other than installing a surge arrestor on the AC side of the inverter to protect my appliances & trying to make sure nothing catches fire in the event of a hit by installing the charge controller and inverter against a concrete wall away from flammable materials. I'm also hoping that my galvanised steel roof will offer some protection by absorbing and diverting most of the energy around the house (but that may just be hopeful thinking). Fuses and breakers offer no protection against lightning as the voltages involved are way to high.

D

Mountain Don · March 2015

CALLD wrote: »

If it's lighting you are concerned about then as Bill said "you don't want it to hit your system in the first place"

I'm also hoping that my galvanised steel roof will offer some protection by absorbing and diverting most of the energy around the house (but that may just be hopeful thinking).

D

Wishful thinking. We were hit this past summer. It was one heck of a thunderstorm. We were not there and I am happy we were not. After the fact lightning maps showed dozens of hits in the very near vicinity. There were scorch marks where lightning danced along the gable ends of the metal roof. Nearly every electrical device that was plugged in was inoperative after the strike, both on the DC and the AC side of things. Real toast with all kinds of bits of silicone and small pieces that rattled when the item was removed, jostled, whatever. At the time the inverter was off,the breaker from batteries to inverter was off. The SPD's (Delta) had the ends blown out. One DC circuit breaker was blown open. It seems like there was more than one direct hit or maybe just one huge one. NOW we have thousands of dollars of protecive air terminals, ground rods and plates and thick braided cables. I do wonder if it will prevent a repeat. (We are in a lightning prone area and were stupid not to install protection when we built. But then I had not heard of anyone in the area being hit either.)

BB. · March 2015

From what I understand, metal roofs and buildings pretty much need the same "lightning protection treatment" as any other wood/concrete/etc. construction would. Metal roofs by themselves do not provide much in the way of protection. Metal is too thin and bonding between metal panels is not "good enough".

-Bill

mike95490 · March 2015

The SPD's (Delta) had the ends blown out. One DC circuit breaker was blown open. It seems like there was more than one direct hit or maybe just one huge one.

Likely a direct hit, to scorch the roof and such. Sadly, you can't put enough SPD's in place to protect against this. Even if you have the Midnight SPD's, it's likely there would just be stubs where the whole thing vaporized. The Delta's are just a sand filled spark gap, and when the metal rods inside vaporize, the pressure blows the cans apart. The wire leads on MOV's are thinner and will vaporize even faster. They will protect in case of a nearby strike, but a direct hit, all bets are for total replacement of everything. Unless you work with Big Electricity, you can't really comprehend how huge even a small lightning strike is. Sometimes even all the copper wire in the walls of the house, is just vaporized and gone !

CALLD · March 2015

mike95490 wrote: »

Unless you work with Big Electricity, you can't really comprehend how huge even a small lightning strike is. Sometimes even all the copper wire in the walls of the house, is just vaporized and gone !

I have to agree there, comparable with other formidable forces of nature like hurricanes, tornados and large hailstorms there isn't much you can do to sleep comfortably during a thunderstorm when you have thousands of dollars worth of electrical equipment on your roof. I've had endless discussions with my wife on lightning protection for our solar equipment and pretty much all have ended with "rather stop worrying about it dear", there isn't much we can do if it happens. My advice is - if you have the means to install a huge lighting rod that equals 2-3 times the height of your house and is located at least 30ft away from it then do it, otherwise you are just hoping for the best...

SPD placement?

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