Lightning, inverter, and grounding

Wxboy
Wxboy Solar Expert Posts: 70 ✭✭✭✭
in General Solar Power Topics #1
The other day during a thunderstorm I was running the tv and Playstation 3 on solar power and suddenly my son said "hey, who turned off the tv"? The inverter had shut off but it came right back on. I realized a few seconds later that I had seen a flash of lightning at the same moment the inverter shut off. The lightning must have been at least a mile away but I wasn't counting the seconds to the thunder so I don't really know how far away it was. Either way it was far from a direct strike. At this time I do not have the inverter, or anything else for that matter, grounded. I bought the grounding rod and have it in the ground but I haven't hooked a ground wire yet because I am planning to move the inverter 30 feet closer to the ground rod and didn't want to run more wire than necessary so I was waiting until I make the move.

My questions are, has anyone ever had this happen before and if my system was grounded do you think this still would have happened?

Second question is after I installed my grounding rod I found the house grounding rod only about 15 feet way. When I do ground everything should it go to the new rod or the house rod. I plan to ground the inverter, panels, batteries, controller, etc.

I currently have a small off grid system that I use to power various things in the house using extension cords. Within the next 6 months I plan to get a Reliance transfer switch to eliminate the extension cords and run a few circuits on solar power on sunny days. The reason I am mentioning this is because I am not sure if the grounding rules change(which ground rod I use) when I start using the transfer switch.

I have a Xantrex Prowatt SW2000 inverter.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Lightning, inverter, and grounding

    This is called "playing with fire", or more accurately "playing with lightning".

    Nothing will prevent damage from a direct strike.

    However, when there are strikes in the area the air gets saturated with stray Voltage. High frequency, high Voltage that can jump from place to place and damage things even though it doesn't make the big flash and deafening roar.

    Grounding helps. If give the equipment some protection. More protection can be had from lightning arrestors properly installed. http://www.solar-electric.com/suprde.html Nothing can provide 100% protection, but you can reduce the risks. You're lucky you only had a temporary outage (momentary increase in the sensed Voltage on the DC side cause the inverter to detect "over Voltage" condition and turn off, most likely).

    Grounding should be to one rod only, or more accurately to a single point (which may be constructed of multiple rods in order to get sufficient contact with Earth). The biggest disagreement here is that the NEC required the panel/mount ground to go in to the house with the DC lines and connect to ground there, whereas most of us prefer that ground be kept outside the building to reduce the risk of introducing the high Voltage to the interior. If the single point ground is outside the structure then everyone should be happy.

    It is unlikely that grounding alone would have prevented your shutdown, but in conjunction with arrestors it would not have happened. That's the trouble with lightning: totally unpredictable in its effect.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Lightning, inverter, and grounding

    i'm a bit confused on why there would be a rod already present if it is a new off grid setup or was the place grid tied/off grid with the ground rod before at one point? what is presently connected to that older ground rod if anything?

    you may have benefited with even placing a temporary wire to the ground rod if the older one is not connected to anything at present.

    if the lightning was truly a mile away and did that to the inverter then you could be in for quite a time with closer strikes. now the ground wire will attach to the grounding point on the back of the inverter and all of the ac lines must not allow for a neutral to ground connection as all shall be kept separate. this could be a problem for some electrical boxes if you plan to wire a plugged wire into the panel for circuit distributions. they like to have the neutral and ground connected there in the electrical box for most electrical services, but you only want that tie point to be at the inverter itself and ground taken off of the designated ground tie point.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Lightning, inverter, and grounding
    niel wrote: »
    they like to have the neutral and ground connected there in the electrical box for most electrical services, but you only want that tie point to be at the inverter itself and ground taken off of the designated ground tie point.

    Once you have settled on what you think is the best possible ground configuration, you can look very hard at adding in surge protectors like those sold by Midnite Solar to protect the AC and DC inputs and output leads so they cannot separately feed damaging voltages and currents into your devices.

    When the ground conductor is the conduit which surrounds the wires it is much less likely that you will get induced voltages between those wires and ground at the devices. Just running a ground next to the wires is not quite as good. Twisting them helps some.
    SMA SB 3000, old BP panels.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #5
    Re: Lightning, inverter, and grounding
    Cariboocoot wrote: »

    However, when there are strikes in the area the air gets saturated with stray Voltage. High frequency, high Voltage that can jump from place to place and damage things even though it doesn't make the big flash and deafening roar.
    I'm pretty sure that the voltage potential which precedes a lightning strike is DC. Lightning is considered high frequency because the strike is essentially a very short duration step function with virtually zero rise time.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Lightning, inverter, and grounding
    ggunn wrote: »
    I'm pretty sure that the voltage potential which precedes a lightning strike is DC. Lightning is considered high frequency because the strike is essentially a very short duration step function with virtually zero rise time.

    I think lightning is still largely not understood - by anyone. Over the course of many years I've read lots of "expert" explanations about what it is and how it functions, including the path being created from ground to sky first before the flash and the latest that the path is created as the flash happens from sky to Earth as electrical pressure forces its way through the atmosphere altering the conductive properties as it goes (and thus creating the zig-zag effect instead of a straight line). Maybe none of it is true. Maybe all of it is true. St. Elmo's fire certainly doesn't look or behave like fork lightning!

    But what I do know from years of living in strike-prone regions and actually seeing what happens is that its behaviour is largely unpredictable in the real world. Logic tells us it should strike the tallest, best-conducting targets first. Yet it can pass by the antenna and hit the ground beside the house, blowing a rock apart in the process.

    The only thing you can be certain about is that it is dangerous and you can not mitigate the effects 100% in all circumstances.
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  • Slappy
    Slappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    #7
    Re: Lightning, inverter, and grounding

    Also with lighting it can produce streamers that doesn't quite make a complete circuit but can still do some damage.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #8
    Re: Lightning, inverter, and grounding
    Cariboocoot wrote: »

    The only thing you can be certain about is that it is dangerous and you can not mitigate the effects 100% in all circumstances.

    I am certain of one additional thing - that I don't want to be anywhere near it when it happens.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Lightning, inverter, and grounding
    ggunn wrote: »
    I am certain of one additional thing - that I don't want to be anywhere near it when it happens.

    You would not like living here, then. :p
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #10
    Re: Lightning, inverter, and grounding
    Cariboocoot wrote: »
    ...
    But what I do know from years of living in strike-prone regions and actually seeing what happens is that its behaviour is largely unpredictable in the real world. Logic tells us it should strike the tallest, best-conducting targets first. Yet it can pass by the antenna and hit the ground beside the house, blowing a rock apart in the process...

    I've witnessed that myself. Several of us were hanging out near the pool a summer or two ago, long after storm clouds had passed over and the sky was nearly completely blue. We had used the 30-minute-no-thunder rule. Suddenly we heard a crack a quarter-mile away as a lightning bolt had traveled probably 10 miles horizontally through blue sky just to hit a tree. That tree was no different than the 10,000 other trees it had passed over on the way. It was so weak it sounded more like a firecracker, and there wasn't any thunder. Truly a bolt out of the blue sky.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • Wxboy
    Wxboy Solar Expert Posts: 70 ✭✭✭✭
    #11
    Re: Lightning, inverter, and grounding
    niel wrote: »
    i'm a bit confused on why there would be a rod already present if it is a new off grid setup or was the place grid tied/off grid with the ground rod before at one point? what is presently connected to that older ground rod if anything?

    you may have benefited with even placing a temporary wire to the ground rod if the older one is not connected to anything at present.

    if the lightning was truly a mile away and did that to the inverter then you could be in for quite a time with closer strikes. now the ground wire will attach to the grounding point on the back of the inverter and all of the ac lines must not allow for a neutral to ground connection as all shall be kept separate. this could be a problem for some electrical boxes if you plan to wire a plugged wire into the panel for circuit distributions. they like to have the neutral and ground connected there in the electrical box for most electrical services, but you only want that tie point to be at the inverter itself and ground taken off of the designated ground tie point.

    Niel, the other ground rod is for the standard house AC wiring. It is just below the meter on the outside of the house. I was thinking the solar components should have a separate ground but I confess to knowing nothing about grounding.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Lightning, inverter, and grounding
    Wxboy wrote: »
    Niel, the other ground rod is for the standard house AC wiring. It is just below the meter on the outside of the house. I was thinking the solar components should have a separate ground but I confess to knowing nothing about grounding.

    Actually they should all be on the same ground rod.
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #13
    Re: Lightning, inverter, and grounding
    Cariboocoot wrote: »
    Actually they should all be on the same ground rod.

    I would just tie the 2 ground rods together if you already have the other rod installed. The more ground rods you have (tied together as one) the better! Especially if you have dry or rocky soil.

    I have 2 ground rods tied together, which are tied to a metal water pipe coming out of the ground. The water pipe was my previous grid, ground tie point. I'm thinking of putting 1 or 2 more ground rods in, for better static discharge and lightning protection.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Lightning, inverter, and grounding
    northerner wrote: »
    I would just tie the 2 ground rods together if you already have the other rod installed. The more ground rods you have (tied together as one) the better! Especially if you have dry or rocky soil.

    I have 2 ground rods tied together, which are tied to a metal water pipe coming out of the ground. The water pipe was my previous grid, ground tie point. I'm thinking of putting 1 or 2 more ground rods in, for better static discharge and lightning protection.

    Even this has to be done the right way. Wires all going to one rod, then that rod connected to the other. Otherwise you create a loop where Voltage can go to the first rod, travel the wire to the second, and then go up any wire connected there and energize equipment.
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #15
    Re: Lightning, inverter, and grounding
    Cariboocoot wrote: »
    Even this has to be done the right way. Wires all going to one rod, then that rod connected to the other. Otherwise you create a loop where Voltage can go to the first rod, travel the wire to the second, and then go up any wire connected there and energize equipment.

    You're referring to the one wire from the equipment I take it. If you put in a Faraday cage around your house, you will have multiple wires coming straight down from above, and they will tie in at different points on the ground network (which is all tied together).
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: Lightning, inverter, and grounding

    Faraday cage, lightning protection, electrical safety ground: three different things meant to handle different situations and not interchangeable.
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #17
    Re: Lightning, inverter, and grounding
    Cariboocoot wrote: »
    Faraday cage, lightning protection, electrical safety ground: three different things meant to handle different situations and not interchangeable.

    Yes, but the faraday cage (or equivalent, ie multiple wires from above) is used for protection against lightning, by diverting the surge away from the equipment and into ground.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #18
    Re: Lightning, inverter, and grounding

    northerner is correct in this case as the tied rods represent one huge ground and not just smaller tied together individual grounds. you may connect electrical equipment to any rod in the case of multiple rods if they are properly tied together.

    use bare #6 and proper ground clamps with the wire buried under the ground. put it as deep as you can so as to avoid accidentally cutting it. i always said at least a foot down, but i believe somebody corrected me saying the nec requires it deeper. i don't remember exactly what was said so somebody can either chime in on that point or you can look it up either online or ask an electrician or your electric utility.
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