PV ground wire size?

rgk1
rgk1 Solar Expert Posts: 135 ✭✭✭
in Solar Beginners Corner #1
Is there a recommended gauge wire (solid?) for the PV to the ground rod? I need to run about 30' from panels to ground rod. Also, does it need to be in conduit or can I just bury it?
4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: PV ground wire size?
    rgk1 wrote: »
    Is there a recommended gauge wire (solid?) for the PV to the ground rod? I need to run about 30' from panels to ground rod. Also, does it need to be in conduit or can I just bury it?

    Normally 6 AWG stranded (bare) wire is use for Earth ground applications. It is run in conduit with other conductors if it is inside where someone might use it as a clothes hanger. For panels, the wire usually just comes down off the roof and goes to the Earth ground rod directly.

    Grounding gets tricky real fast. Even the "experts" argue about how it should be done. One thing they agree on is that all equipment (including panels) grounds should tie to one Earth ground point only. And remember that this is a safety ground, not lightning protection. That's another rat's nest of discussion.
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #3
    Re: PV ground wire size?

    I have #2 stranded (indoors) from the ground bus to the ground rod. My panels are ground mounted. I have conduit run underground from the panels to the shed and the PV + - run through it. So, should I still use #6 stranded and run it inside the conduit with the PV leads, or is solid ok and run it outside the conduit?
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: PV ground wire size?

    You can use solid, it's just easier to work with stranded on the large gauge wires.

    How far from the ground rod are your panels? If they're far away (how far is another heated debate topic) you can drive a second ground rod at the panel installation.

    Otherwise bring it through the conduit with the other wires and hook it to the common point.

    (Now let's see how much disagreement this generates. :p )
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #5
    Re: PV ground wire size?

    My panels are 30 feet from the ground rod. I don't want to use another ground rod as my solar setup has one and there is on on the house about 20 feet away. I am going to tie those two rods together. That seems to be the recommended way from what I have read.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: PV ground wire size?
    rgk1 wrote: »
    My panels are 30 feet from the ground rod. I don't want to use another ground rod as my solar setup has one and there is on on the house about 20 feet away. I am going to tie those two rods together. That seems to be the recommended way from what I have read.

    Whoa. Hold on there.
    If there's already a ground rod at the array site, ground the panels to that.
    Do not ground the panels to that and then run an additional ground wire to the other ground rod.
    That would create one of the notorious "ground loops" you may have heard about; giving any stray current that might connect with the ground wire an alternate path to flow through and avoid being sunk to ground.

    When you hear about connecting two ground rods together the purpose is to increase contact with the Earth to lower the resistance for sinking current. It has to be done in the proper way, which is that all system grounds connect to one rod, then that rod connects to any other rods.
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #7
    Re: PV ground wire size?

    No ground rod at the panels. The panels are 30 ft from the shed where the solar equipment and a ground rod is located. The other ground rod is at the house - 20 ft from the shed and 50 ft from the panels. That ground rod is the homes electrical ground rod. My home and my solar are completely separate systems that share nothing except the proximity of their ground rods. Suggestions?
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: PV ground wire size?

    Totally separate? As in no connections between the two whatsoever, including AC neutral, AC hot, and AC ground? If so, keep it that way; don't connect the ground rods of the two systems.

    The only time you need multiple ground rods connected together is if the soil resistance is too high to get good conductance with one. This situation is usually found in dry locales and rocky/sandy soil.
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #9
    Re: PV ground wire size?

    Correct. No connections between them whatsoever. If I want the solar to power anything in the house, I have 2 inlet boxes on the side of the house. They each go to a single outlet in the house. One in the kitchen and one in the master bedroom. Even those are in no way connected to the homes wiring system. You could think of it as an extention cord without having to open a door or window. Am I good to connect a solid #6 from the panel to the rod that the rest of the solar uses and can I just direct bury it all the way from the panels to the rod? A little off the subject but while I'm asking questions... voltage drop from the panels I understand. Plenty of topics on that. But I can find nothing about whether or not there is amperage drop in a wire run as it relates to distance from panel to charge controller. I have 2 panels and wasn't sure whether to up the amperage or the voltage to the controller. Decided to go with higher voltage and let the CC do the conversion.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: PV ground wire size?

    I'd say "yes" to connecting the panel frame ground to the same ground rod the rest of the solar equipment is connected to.

    But don't direct bury ordinary wire; it will corrode and decay in the ground without protection. There is wire rated "UG" which can be direct buried, but I don't think you'll find that in #6 stranded or solid; it's usually two conductor cable.

    Amperage drop? Not in the same sense of the Voltage drop where you can measure "X" Volts at the source and "X-1" Volts at the other end even without a load. Amps are the flow through a circuit, and if the circuit is consistently sized all around it's the same Amps everywhere. What you do get is a drop in the over-all Amps when the wire loses too much Voltage. This is because of the reason why the Voltage drops: more wire = more resistance. Increase the resistance in a circuit and the current goes down.

    Have a look at this wire gauge chart: http://www.powerstream.com/Wire_Size.htm
    You'll see one category labeled "Ohms per 1000 ft." Smaller wire = greater resistance. Longer distance = greater resistance. Increase resistance, Voltage goes down over distance and current is likewise reduced. If you just push the Voltage up higher it overcomes the resistance and the current goes up. That's why you have to consider Voltage, current, type of power (yes), and distance when calculating wire size.
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #11
    Re: PV ground wire size?

    Thank you for the the help. It is greatly appreciated.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #12
    Re: PV ground wire size?
    Cariboocoot wrote: »
    Whoa. Hold on there.
    If there's already a ground rod at the array site, ground the panels to that.
    Do not ground the panels to that and then run an additional ground wire to the other ground rod.
    That would create one of the notorious "ground loops" you may have heard about; giving any stray current that might connect with the ground wire an alternate path to flow through and avoid being sunk to ground.

    When you hear about connecting two ground rods together the purpose is to increase contact with the Earth to lower the resistance for sinking current. It has to be done in the proper way, which is that all system grounds connect to one rod, then that rod connects to any other rods.
    Been following this thread and it pertains to me also. I am going to move my solar arrays on top of pole racks about 350 ft from where the inverter is because of shading. If I ground the panels at the solar panels, do I only need to run the 2 DC positive and negative wires the 350 ft. to inverter? In the present location the panels are grounded at the mount and onlt 2 wires went to the inverter. It passed inspection that way. :Dsolarvic:D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: PV ground wire size?
    solarvic wrote: »
    Been following this thread and it pertains to me also. I am going to move my solar arrays on top of pole racks about 350 ft from where the inverter is because of shading. If I ground the panels at the solar panels, do I only need to run the 2 DC positive and negative wires the 350 ft. to inverter? In the present location the panels are grounded at the mount and onlt 2 wires went to the inverter. It passed inspection that way. :Dsolarvic:D

    350 feet between grounding rods should be more than enough to satisfy anyone's definition of "far away". :D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
    Re: PV ground wire size?
    Cariboocoot wrote: »
    Whoa. Hold on there.
    If there's already a ground rod at the array site, ground the panels to that.
    Do not ground the panels to that and then run an additional ground wire to the other ground rod.
    That would create one of the notorious "ground loops" you may have heard about; giving any stray current that might connect with the ground wire an alternate path to flow through and avoid being sunk to ground.

    When you hear about connecting two ground rods together the purpose is to increase contact with the Earth to lower the resistance for sinking current. It has to be done in the proper way, which is that all system grounds connect to one rod, then that rod connects to any other rods.

    coot may sound a bit confusing here on the way ground rods are to be connected. ground rods can be interconnected via large sized bare copper wire that is run underground. i disagree with interconnecting these rods above ground. a conflict arises due to an nec requirement to have a ground lead present with the pv leads going back to the inverter. that would create the secondary path to ground and potential ground loops as well as allow lightning and emp to needlessly enter a home and hence my disagreement with this nec rule. the best and safest would be to connect the rods together underground and forget the ground wire requirement going into the house with the pv leads. the nec's way you have to forget the underground interconnection with a ground lead going the distance into your house and then to ground and is not as safe as the underground connection. imho, the nec is protecting their ability to make and impose rules and is not necessarily protecting us in the best possible manner.

    solarvic,
    i think you'll be ok not running an underground wire connecting the rods. i'm surprised they didn't fail your system for not having the ground wire going back to the inverter with the pv leads. imho you can leave it out of the equation as you don't want to bring lightning or emp into your house because the path to ground goes through it.
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  • solarpat
    solarpat Registered Users Posts: 5
    #15
    The reasons code requires the ground from the solar array to the inverter at the house is number 1 it is a "separately derived service' and that requires a gec. grounding electrode conductor, also they want the potential everywhere at the house and the array to be 0, also code states that the grounds are to be ran with the PV conducters, so in case you get a ground fault from the conductors you won't energize the pipe or the ground. I live in oregon and I know that requirements vary some with the states statutes. I remember when I was doing a VA hospital in New York that they ran #10 grounds all through the array and that was all that was required, in oregon the smallest gec is #6
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