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I'm putting together a Solar array, grid tied. (50) 200 watt panels on the roof. Couple questions:


As far as V/D goes, would you keep the a/c runs as short as possible or the d/c runs as short as possible?

Also, what's the best way to enter the roof with (50) 10/2's?
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  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar

    Also, I'm curious as to what keeps the system from backffeding utility if there is a power outage
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Solar
    Also, I'm curious as to what keeps the system from backffeding utility if there is a power outage

    All grid-tie inverters have an "anti-islanding" feature which causes them to shut down when they sense there's no grid to synch to.

    Usually the longest runs are on the DC side, as it has the highest Voltage and therefore the lowest drop over distance.

    You probably won't have 50 10/2's entering the roof anywhere, as the panels will largely be connected in series to create the aforementioned high Voltage array. I don't know your panel specs or your intended inverter but I'm sure the "Grid-Tie Guys" here can give you some idea as to sample systems. :D
  • dsp3930
    dsp3930 Solar Expert Posts: 66 ✭✭✭✭
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    Re: Solar

    Welcome. :D

    You are about to take on a fairly large project both in dollars and scale. The nature of your questions lead me to believe you may want to do some more looking and researching before you jump in. We all started where you are at some point. It takes a while to soak up all the informaiton needed to do one of these systems yourself.

    As to AC vs DC runs ....
    Solar panels output DC. You would only be using AC runs if using something like an Enphase micro-inverter on each panel. The output would then be AC from each panel that is then combined and routed via one main run to your main panel.

    Assuming your are not going with micro inverters ....
    Each panel is combined in series strings (up to the controller/inverter max voltage) and then those strings are wired in parallel to a combiner box. The combiner with DC breakers would typically also be on the roof or side of your house. Each string then ties into that combiner and one single run of wire is routed to the GT inverter or charge controller.
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    All grid-tie inverters have an "anti-islanding" feature which causes them to shut down when they sense there's no grid to synch to.

    Usually the longest runs are on the DC side, as it has the highest Voltage and therefore the lowest drop over distance.

    You probably won't have 50 10/2's entering the roof anywhere, as the panels will largely be connected in series to create the aforementioned high Voltage array. I don't know your panel specs or your intended inverter but I'm sure the "Grid-Tie Guys" here can give you some idea as to sample systems. :D

    The panels come with 100' leads and mc4 connectors. They go the combiner. Unless this combiner is on the roof, I was thinking all the leads would come indoors. The equipment is not onsite yet. They come with detailed prints and schematics, but I do not have my hands on them yet.
    dsp3930 wrote: »
    Welcome. :D

    You are about to take on a fairly large project both in dollars and scale. The nature of your questions lead me to believe you may want to do some more looking and researching before you jump in. We all started where you are at some point. It takes a while to soak up all the informaiton needed to do one of these systems yourself.

    As to AC vs DC runs ....
    Solar panels output DC. You would only be using AC runs if using something like an Enphase micro-inverter on each panel. The output would then be AC from each panel that is then combined and routed via one main run to your main panel.

    Assuming your are not going with micro inverters ....
    Each panel is combined in series strings (up to the controller/inverter max voltage) and then those strings are wired in parallel to a combiner box. The combiner with DC breakers would typically also be on the roof or side of your house. Each string then ties into that combiner and one single run of wire is routed to the GT inverter or charge controller.


    We have the leads from the panels going to a combiner, then a ground fault interupter, and from there it goes into theSunnyboy sb8000us inverter. From the inverter on it WILL be A/C. I was wondering if I should keep the D/C leads as short as possible,or the a/c side. It's only a matter of 100' but I still want optimum performance.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Solar

    Okay the Sunnyboy has an array Voltage of 240-480 VDC. So if you were using Evergreen 205 Watt panels for example (Vmp 18.4) they would probably be wires as two parallel strings of 25 panels in series. The Vmp to the inverter would then be 460 VDC and there would only be two strings to combine. You could indeed run the wire from each string into the house before combining them.

    Just an example; not an actual installation recommendation. :D
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
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    Re: Solar

    I have 8 strings of 9 panels with the combiner in the attic. This is how the installer got it inside.
  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
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    Re: Solar
    We have the leads from the panels going to a combiner, then a ground fault interupter, and from there it goes into theSunnyboy sb8000us inverter. From the inverter on it WILL be A/C. I was wondering if I should keep the D/C leads as short as possible,or the a/c side. It's only a matter of 100' but I still want optimum performance.

    The Sunny boy has an internal ground fault interupter. Why add another?
  • dsp3930
    dsp3930 Solar Expert Posts: 66 ✭✭✭✭
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    Re: Solar

    You would not have 100' leads running from each panel to the combiner. (unless that was a typo) It would be just be the POS/NEG/GROUND from each end of the two strings to the combiner. Then one POS/NEG/GROUND to the GT inverter.

    You are going to have a high voltage / low amps on the DC circuit.
    I'd say that the DC side would be the better place for the longer run, but it just depends on where a suitable mounting location is for the combiner and inverter.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Solar

    You did not tell us the brand/model of solar panels--It does affect the details of the install.

    Basically, you are going to (roughly) place 10 panels in series for a Vmp-array of ~345 volts. For your 50 panels, that would be 5 parallel connected strings in to a single 5 input combiner box (although the Sunny Boy may have some sort of combiner itself--so it could be wired slightly differently). You may put the combiner on/near the roof and run one pair of DC wires to the inverter--Or you may run the five pairs of strings to the combiner mounted next the the inverter. Which ever is easier for you.

    Also, even though you can mount the combiner/inverter in full sun/weather--It would be nicer if they are in an area shielded from full sun/driving rain.

    Who did the "engineering" for the system? You have electrical planning/configuration (solar panels need to be configured to series/parallel voltage/current) to match the limited input operational range of the inverter (~300-480 VDC). As well as probably needing the sign-off from a professional engineer if the panels are mounted on the building.

    Do you have the tools / parts to make up your own MC4 crimp connections?

    -Bill

    PS: Here is a photo heavy thread on installing an 8kW GT system:

    Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    -BB
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    Jburgess wrote: »
    The Sunny boy has an internal ground fault interupter. Why add another?

    The prints show it seperate, but it could be internal. I have not seen the equipment yet.
    dsp3930 wrote: »
    You would not have 100' leads running from each panel to the combiner. (unless that was a typo) It would be just be the POS/NEG/GROUND from each end of the two strings to the combiner. Then one POS/NEG/GROUND to the GT inverter.

    You are going to have a high voltage / low amps on the DC circuit.
    I'd say that the DC side would be the better place for the longer run, but it just depends on where a suitable mounting location is for the combiner and inverter.


    Thanks. That makes sense and will be much easier to deal with.
    BB. wrote: »
    You did not tell us the brand/model of solar panels--It does affect the details of the install.

    Basically, you are going to (roughly) place 10 panels in series for a Vmp-array of ~345 volts. For your 50 panels, that would be 5 parallel connected strings in to a single 5 input combiner box (although the Sunny Boy may have some sort of combiner itself--so it could be wired slightly differently). You may put the combiner on/near the roof and run one pair of DC wires to the inverter--Or you may run the five pairs of strings to the combiner mounted next the the inverter. Which ever is easier for you.

    Also, even though you can mount the combiner/inverter in full sun/weather--It would be nicer if they are in an area shielded from full sun/driving rain.

    Who did the "engineering" for the system? You have electrical planning/configuration (solar panels need to be configured to series/parallel voltage/current) to match the limited input operational range of the inverter (~300-480 VDC). As well as probably needing the sign-off from a professional engineer if the panels are mounted on the building.

    Do you have the tools / parts to make up your own MC4 crimp connections?

    -Bill

    PS: Here is a photo heavy thread on installing an 8kW GT system:

    Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    -BB


    Thanks alot, I appreciate the photos. The system was bought as a complete system fully engineered. I'll be able to post much more info when I get back to the office. I do not have a crimper, but I will aquire one for this job. Thanks for the heads up.
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    solar_dave wrote: »
    I have 8 strings of 9 panels with the combiner in the attic. This is how the installer got it inside.

    Great idea, I think that's the way to go. Thanks
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    BB. wrote: »
    You did not tell us the brand/model of solar panels--It does affect the details of the install.

    Basically, you are going to (roughly) place 10 panels in series for a Vmp-array of ~345 volts. For your 50 panels, that would be 5 parallel connected strings in to a single 5 input combiner box (although the Sunny Boy may have some sort of combiner itself--so it could be wired slightly differently). You may put the combiner on/near the roof and run one pair of DC wires to the inverter--Or you may run the five pairs of strings to the combiner mounted next the the inverter. Which ever is easier for you.

    Also, even though you can mount the combiner/inverter in full sun/weather--It would be nicer if they are in an area shielded from full sun/driving rain.

    Who did the "engineering" for the system? You have electrical planning/configuration (solar panels need to be configured to series/parallel voltage/current) to match the limited input operational range of the inverter (~300-480 VDC). As well as probably needing the sign-off from a professional engineer if the panels are mounted on the building.

    Do you have the tools / parts to make up your own MC4 crimp connections?

    -Bill

    PS: Here is a photo heavy thread on installing an 8kW GT system:

    Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    -BB

    The equipment arrived today. It looks like (45) 190w polycrystalline photovoltaic
    solar panels, so I think I'll configure (3) groups of (15) strung together. I have a DC-disconU-2 (disconnect) that I will mount under the Sunnybuy 8000. From there I will hit my A/C disconnect, and then from disco I'll feed into a 200 amp ML panel, using a breaker and hold down kit. One question is inside there are only lugs, nothing for the MC4 connectors to attach to. Do you buy short whips with leads?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Solar

    If you do not have the tooling, yes, purchasing male/female jumpers and cutting them in 1/2.

    MC Jumpers


    And, again have you confirmed with somebody the series/parallel connections of your panels? The Vmp/Imp and Voc/Isc are important parameters--without knowing them (and exactly which inverter you are using)--It is most likely that you will not be able to "guess" at the proper series/parallel connections.

    Many vendors offer on-line calculators that with panel information and your local min/max temperatures will give you supported configurations.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    BB. wrote: »
    If you do not have the tooling, yes, purchasing male/female jumpers and cutting them in 1/2.

    MC Jumpers


    And, again have you confirmed with somebody the series/parallel connections of your panels? The Vmp/Imp and Voc/Isc are important parameters--without knowing them (and exactly which inverter you are using)--It is most likely that you will not be able to "guess" at the proper series/parallel connections.

    Many vendors offer on-line calculators that with panel information and your local min/max temperatures will give you supported configurations.

    -Bill


    I'll be on their website tonight with the online calculator. I was looking at the links you posted earlier, and I was wondering, When I ground the frames and rails, shouldn't I take the solid ground wire into the service panel, rather than the Sunnyboy? The op mentiond they go to inverter, but to me that would seem like "directing" a lightning strike into your inverter. What do you think?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Solar

    I have my opinions about lightning--but I am not an expert or involved with code:
    BB. wrote: »
    A couple threads about Lightning:

    Off Grid Grounding Technique?
    Another Question, this time about Lightning

    Note, the above are discussions, not a do A, B, and C--and you will be "safe". There probably is no such thing with lightning. Several different techniques are discussed--and a few of those posters even have experience with lightning. :cool:

    And our host's consolidated FAQ page:

    www.windsun.com
    Lightning Protection for PV Systems

    From other past posts here, Windsun (admin/owner of NAWS), he said that most of lighting induced failures he saw were in the Inverters' AC output section.

    The bare ground wire should go down the outside of the frame / pole work to the "earth ground" (rods, plates, etc.). There should be no reason to bring a "green wire" from the solar array into the DC side of the inverter from your pole mount to the inverter directly.

    If you choose to run buried copper from the pole to the home--terminate it at the ground rod (typically) near your service entrance. I would not bring the bare wire from the array to your service panel (don't bypass the ground rod)... My worry is that you would run the risk of bring more lightning energy into the house that way.

    The ground rod should be your one "common ground bus" point for all of your AC/DC/Safety Grounds (water pipe, gas pipe, phone, cable, etc.).

    Although, running the two DC and safety ground as one cable set is done for roof mounted arrays in our area. + / - and green wire from array frame grounding, cable down through EMT conduit to the junction box of the GT inverter. Attach +/- to DC Bus Connections. Tie ground/green wire with the rest of the normal house green wire(s) / box safety grounds, and follow normal wiring procedures).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    BB. wrote: »
    I have my opinions about lightning--but I am not an expert or involved with code:



    The bare ground wire should go down the outside of the frame / pole work to the "earth ground" (rods, plates, etc.). There should be no reason to bring a "green wire" from the solar array into the DC side of the inverter from your pole mount to the inverter directly.


    THANK YOU. I misunderstood the op from the other link. I agree 100%


    If you choose to run buried copper from the pole to the home--terminate it at the ground rod (typically) near your service entrance. I would not bring the bare wire from the array to your service panel (don't bypass the ground rod)... My worry is that you would run the risk of bring more lightning energy into the house that way.


    That makes perfect sense. The building right now does not have ground rods, only a concrete encased electrode. 250.52 (a) (3). So, there's just a #4 solid coming out of the foundation. This will land in the service panel. How does that affect your answer? Or should I still drive 2 rods, bond them with the #4, and then on to the service panel? That seems like the best option.


    The ground rod should be your one "common ground bus" point for all of your AC/DC/Safety Grounds (water pipe, gas pipe, phone, cable, etc.).

    That's what I'll do. Thanks alot

    Although, running the two DC and safety ground as one cable set is done for roof mounted arrays in our area. + / - and green wire from array frame grounding, cable down through EMT conduit to the junction box of the GT inverter. Attach +/- to DC Bus Connections. Tie ground/green wire with the rest of the normal house green wire(s) / box safety grounds, and follow normal wiring procedures).

    -Bill

    It came with double insulated cables with mc4 connectors. Do they need to be in conduit?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Solar

    from what i understand is that mr. wiles wants a ground lead brought directly into the house with the pv leads even if you had grounded it at the pole (or whatever other location is involved) and buried a bare ground wire to the main rod. i too say burial of an interconnecting ground wire to the main home ground rod is the only correct answer if one does not wish to lead lightning into one's home and the advent of this extra wire mr. wiles cites will create ground loops when one incorporates the underground ground wire too. he never indicated at any time that an underground ground wire was even a possibility let alone a better solution.
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    niel wrote: »
    from what i understand is that mr. wiles wants a ground lead brought directly into the house with the pv leads even if you had grounded it at the pole (or whatever other location is involved) and buried a bare ground wire to the main rod. i too say burial of an interconnecting ground wire to the main home ground rod is the only correct answer if one does not wish to lead lightning into one's home and the advent of this extra wire mr. wiles cites will create ground loops when one incorporates the underground ground wire too. he never indicated at any time that an underground ground wire was even a possibility let alone a better solution.

    The ground lead you bring into the home, that would land in the service panel, not the inverter, correct?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Solar

    For my Xantrex GT setup (panels on roof, short run to GT inverter)--The green wire ends up in the GT safety ground (green screw) connection.

    If I lived in an area with heavy lightning activity--I would take the solar panel frames and mounting rail ground wires directly down the side of my home to a ground rod next to the house. And I would also tie that ground rod to my main ground rod (service entrance) because my main ground rod is the front of my home and the solar array is at the rear of my home.

    This is based on my limited understanding that lightning strike energy wants to spread to the outside edges of the home, not go down through the center ("skin effect").

    Running a ground wire between the two (or more rods), makes it "safe" for AC electrical grounding (all possible AC/DC ground rods/runs are electrically connected).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    BB. wrote: »
    For my Xantrex GT setup (panels on roof, short run to GT inverter)--The green wire ends up in the GT safety ground (green screw) connection.

    If I lived in an area with heavy lightning activity--I would take the solar panel frames and mounting rail ground wires directly down the side of my home to a ground rod next to the house. And I would also tie that ground rod to my main ground rod (service entrance) because my main ground rod is the front of my home and the solar array is at the rear of my home.

    This is based on my limited understanding that lightning strike energy wants to spread to the outside edges of the home, not go down through the center ("skin effect").

    Running a ground wire between the two (or more rods), makes it "safe" for AC electrical grounding (all possible AC/DC ground rods/runs are electrically connected).

    -Bill


    Thanks Buddy, I appreciate that. I was onsite today and got all the rails mounted on the roof.

    Question: Each set of panels are mounted on two rails. It called for a minimum of #8 to ground the rails, but the lugs would accept up to a # 4 so that's what I used. The bigger the better for moving fault current or lightning strikes. My question is, each panel mounts on two rails, does my ground need to hit both of those rails for each string? or can it hit only one rail, and effectively would count on the bolted connections through the panel to ground the second rail. I plan on running that # 4 solid down the back of the roof, drive at least 4 8' copper ground rods, 8' apart, and bond the #4 to the rods all the way back to the service, and bond that wire to the concrete encased electrode. That sound like a good way to do it. What do you think?
  • drees
    drees Solar Expert Posts: 482 ✭✭✭
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    Re: Solar

    Typically every single piece of rail (and each panel unless using WEEBs) needs to have a ground lug attached and be connected to your continuous ground wire.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Solar

    i think it's the pv frame that needs grounded and not the rails. it doesn't hurt with grounding the rails too, but the pv frames are above the rails and are first in line for any faults or lightning. the rails are also electrically connected to the pv frames and if for any reason they aren't, it would then be my opinion to ground it specifically and imho does not need to be continuous as the pv frames are as i would then split bolt a piggyback connection from the rails to the main ground wire. but that's what i would do, or should i say, recommend. technically as i said the frames are above the rails and, in a sense, cover and protect any metal laying below.
  • drees
    drees Solar Expert Posts: 482 ✭✭✭
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    Re: Solar

    Hmm - thought both rails and panels had to be grounded - but maybe I'm mixed up because I'm used to using WEEBs to ground the panels to the rails.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Solar

    i know that there was a poster that the inspector made him ground the rails, but unless somebody can show me in the nec rules i don't believe it to be normally required. i could be wrong, but i feel it is not necessary even if wiles did brainstorm another blunder.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Solar

    IIRC, it is part of code to eclectically ground all metal surfaces and mechanical support structures. I had to do this with computers systems too (ground braid across a metal hinge to the metal door). We could not use the "incidental" grounding of a metal hinge. Also, we had to use wire jumpers instead of the 1/2" metal bolts that held the frames together too. :roll:

    The idea being that somebody unbolting a major structure/exterior element could not accidentally un-ground a piece of metal--which could become a shock hazard (if an exposed wire, for example, fell on the ungrounded metal panel).

    The ground bonding wire was a separate electrical connection (properly marked) that would only be disconnected after the power was removed from the system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Solar

    incidental grounding is not what this is and they'd have to unbolt all of the bolts from the pvs to the rails and then remove the pvs to unground the rails. highly unlikely. there is a higher possibility of the main ground lead breaking before those rails would be ungrounded and the pv being over the rails not only prevents a stray wire from a pole hitting the rails, but also acts a bit like a small faraday shield as no lightning is hitting those rails before hitting the pv frames first. at best, as i said, you could jumper it to the main ground lead via a split bolt if one wants it grounded even further. if wiles is that concerned of metal underneath a grounded pv frame then why would he have it lead straight into the house anyway? it's ridiculous.:roll:
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    niel wrote: »
    incidental grounding is not what this is and they'd have to unbolt all of the bolts from the pvs to the rails and then remove the pvs to unground the rails. highly unlikely. there is a higher possibility of the main ground lead breaking before those rails would be ungrounded and the pv being over the rails not only prevents a stray wire from a pole hitting the rails, but also acts a bit like a small faraday shield as no lightning is hitting those rails before hitting the pv frames first. at best, as i said, you could jumper it to the main ground lead via a split bolt if one wants it grounded even further. if wiles is that concerned of metal underneath a grounded pv frame then why would he have it lead straight into the house anyway? it's ridiculous.:roll:



    The rails all connect with a ground washer.It's listed for grounding, outdoor use, and for use with solar. It did off WEEBS as "options" in the parts summary. Are the WEEBS required? I thought the purpose of using this grounding clip on all the bolted connections was to not have to also use WEEBS.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Solar

    do understand that i am not an expert on the nec rules, but i love to poke holes at some aspects of the nec because it isn't always done in a common sense manner. ultimately your local inspector has the final say so and he can give his opinion on your matter. the nec is often the basis for local laws, but local lawmakers interpret and do what they will as the nec is not a law making body. your inspector may chose to overrule an aspect of the nec even if they have adopted it as law.
  • McClary's Electrical
    McClary's Electrical Registered Users Posts: 21
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    Re: Solar
    niel wrote: »
    do understand that i am not an expert on the nec rules, but i love to poke holes at some aspects of the nec because it isn't always done in a common sense manner. ultimately your local inspector has the final say so and he can give his opinion on your matter. the nec is often the basis for local laws, but local lawmakers interpret and do what they will as the nec is not a law making body. your inspector may chose to overrule an aspect of the nec even if they have adopted it as law.

    Well said, I deal with that alot. I'll keep you updated how it goes.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Solar

    yes, i am sure i and many others would like to know how it turns out and feel free to copy this thread and show it to him. he may feel i have a valid argument or just opt for the same old regulations first and common sense later approach of mr. wiles.