Ground wire from PV to Controller

jcheiljcheil Solar Expert Posts: 722 ✭✭✭
I know the discussion has gone back and forth regarding if a ground rod should be installed at the PV "AND" at the inverter and if they should be connected together, etc.

My question is per the wiring diagram outback provides, they show only one ground rod, at the inverter. They show a ground wire coming from the PV to the ground rod at the inverter. I have my existing wires coming from the PV combiner to the controller/inverter in a pipe. My existing frame ground at the pv goes to its own ground rod there at the pv. I am going to change it and follow what is shown on the outback diagram and bring it back to the inverter/controller ground rod.

My question is: I will be running a #6 bare (because I have a free 500' roll of it laying around) and was wondering if I can just direct bury that or if it has to be in the pipe with the other wires? Again, I am removing the ground rod at the PV per Outback (but leaving the SPD on the PV combiner). Hope that is the wise thing to do.
Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html

Comments

  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Ground wire from PV to Controller

    I did it like you have it now. If you change and you care, I have seen threads discuss that some codes say it has to be in the conduit. I know nothing. Just had seen that post.
    gww
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Ground wire from PV to Controller

    Oh god, I just read the recent post http://forum.solar-electric.com/showthread.php?24475-Lightning-and-inverter&p=200013#post200013 and the thread from 2009 shown in that thread and now I am COMPLETELY confused as to what is the best thing to do.

    For lightning, it almost makes senses to NOT connect your PV ground to anything at the "house". Maybe I should just leave the PV frames on their own ground rod the way they are with the SPD there? Ugh...

    PS - For clarification, my setup now is the PV array is about 60' from my (new) "Power House" which is about 120' away from my (living) "House". I just feed the 240v from the power house to the main house. The N-G bond is in the powerhouse. I did this change (the new power house) because with the much larger new battery bank I am installing, I wanted it far away from the house in case something went boom. Previously, the batteries were in a power room on the other side of my bedroom wall :)
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: Ground wire from PV to Controller

    Yes--Lightning is a tough animal to control.

    I think most people do not want to disconnect their power lines and roll them back 10-20' from the home.

    I used to think that a single point Neutral+Earth Ground bond (in the AC main panel) was the answer...

    These days, I (think I) believe that you should have Neutral+Earth Bonds at each distributed panel (i.e., one at home, a second in the milking barn, a third at the well head, etc.).

    You want the ground to be "ground" where you are using the power. It is easy to have volts to dozen of volts between two ground rods driven 100' apart--Espeically in a "quasi-industrial" environment with lots of motors and pumps (and AC leakage current).

    The idea of the "pure/ideal" ground at the house panel and running that all over a large installation just does not happen in real life. The grounding issues are all "local"--That is where it matters.

    Sometimes there are "mistakes"--Such as a pole that had the 120/240 VAC neutral grounded (at the pole) and at the home one of the hot wires was grounded (or vice-verse--don't remember). The problem was found after the first snow fall and the snow was melting around the ground rod from heating because of the improper neutral bonding.

    Add the Midnite SPD's at each panel / point where wires enter or leave the building (with SPD's attached to local earth ground/ground ring)--Not sure what else is practical.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Ground wire from PV to Controller

    OK, so let me see if I got this. You are saying, best practice would be:

    PV Frames tied together to a ground rod at the PV combiner and that ground wire connected to the N-G bond at the Inverter Panel in the powerhouse.

    Then the inverter panel in the powerhouse feeds 4 conductors (2 hot, 1 neutral and 1 ground) to the main panel of the house where it is ALSO bonded N-G and connected to another ground rod there?
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Ground wire from PV to Controller

    Something people don't seem to get about grounding: location, location, location.

    It makes a difference where the single ground point is in respect to the items being grounded.

    Best-case scenario that fits NEC and reduces the chance for PV grounding to introduce lightning to the home: ground rod outside house (usually near service entrance). Ground wire for PV comes down house, ties to rod there. Another wire comes off rod and goes into house to 'pick up' what needs grounding within.

    When the physical layout of components changes then the way the wiring is run changes and the needs/solutions change. If the PV is far away from the ground rod a separate rod may be used to ground it.

    I also agree with SG that there's about zero chance that PV is going to cause a safety issue with frames and mounts; grounding them is more a matter of protection against stray Voltage. As such they don't really need to be grounded. This is where two of the reasons for grounding come together and blur: safety & lightning. Unfortunately the NEC doesn't see it that way and has the grounding requirement (or did yesterday; never can tell with them).

    The problem with all lightning protection is that unlike power systems lightning doesn't have fixed values. You do not know the Voltage, intensity, or frequency and so it is impossible to say "this will handle it". You can get a direct strike which nothing will handle, and you can get a direct strike which is actually very low power and does no damage. Mostly we are trying to minimize the damage from the stray Voltage which energizes things around strikes, not the strikes themselves.

    Grounding should be done for safety purposes first. That is; if something goes wrong will someone touching an exposed surface create a better circuit path than the wire? You want to avoid shocks and electrocution (which takes surprisingly little power). Don't even think about lightning when considering this.

    Second would probably be for RF reduction, which can be a problem with PV systems (especially OG) because the switching can generate quite a bit of variable frequency. Lightning issues come in third in my opinion, and keep in mind I live somewhere that is prone to strikes. If strikes are not an issue where you are, don't worry about it.
  • Organic FarmerOrganic Farmer Solar Expert Posts: 128 ✭✭
    Re: Ground wire from PV to Controller
    jcheil wrote: »
    OK, so let me see if I got this. You are saying, best practice would be:

    PV Frames tied together to a ground rod at the PV combiner and that ground wire connected to the N-G bond at the Inverter Panel in the powerhouse.

    Then the inverter panel in the powerhouse feeds 4 conductors (2 hot, 1 neutral and 1 ground) to the main panel of the house where it is ALSO bonded N-G and connected to another ground rod there?

    Yes, I believe that is 'best practice'.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Ground wire from PV to Controller

    No!

    Under no circumstances do you want a system with two N-G bonds in it.
  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: Ground wire from PV to Controller
    No!

    Under no circumstances do you want a system with two N-G bonds in it.

    And that is something I would debate.

    In my area, there is a neutral ground bond at the pole and a neutral ground bond at each of the 6 homes sharing that transformer. Multiple grounding there. ... Why not past the main panel?

    Clarification: bring the ground wire to the next ground rod, not to the next panel ground bus then to the ground bus.

    Don't bring lighting into the building.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Ground wire from PV to Controller
    BB. wrote: »
    And that is something I would debate.

    In my area, there is a neutral ground bond at the pole and a neutral ground bond at each of the 6 homes sharing that transformer. Multiple grounding there. ... Why not past the main panel?

    Clarification: bring the ground wire to the next ground rod, not to the next panel ground bus then to the ground bus.

    Don't bring lighting into the building.

    -Bill

    Debate if you like Bill, but the two situations are different.
    The ground at the pole does not then travel as a separate wire and connect to your house ground. No potential circuit is formed of neutral & ground wiring with two bonds between them at different locations.
    You may as well say that every house fed from the same power transformer has an N-G bond too that it doesn't matter.
    In practice it does, although you only notice when something goes wrong (which is so often the case with these things).
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Ground wire from PV to Controller
    BB. wrote: »
    And that is something I would debate.

    In my area, there is a neutral ground bond at the pole and a neutral ground bond at each of the 6 homes sharing that transformer. Multiple grounding there. ... Why not past the main panel?

    Clarification: bring the ground wire to the next ground rod, not to the next panel ground bus then to the ground bus.

    Don't bring lighting into the building.

    -Bill

    Bill,
    The problem is that current flowing over multiple paths in the grounded conductor (MGN) and in the individual ground electrodes on the POCO side of your service will not generally cause any harm and more importantly it is the standard for utility wiring in the US.
    Now, once you pass the service disconnect the NEC mandates that you split the function up into two separate conductors, the grounding conductor (EGC) and the grounded conductor (typically a neutral).
    The only metal return path for current from that point to the transformer is over the POCO neutral with the ground electrode system (GES) on your end and the POCO side forming an alternate, relatively high resistance path.
    The EGC is meant to carry current only in the event of a wiring or equipment fault.
    If you make a second bond between EGC and neutral, for example at a sub panel, there will be two metallic paths for the neutral current to follow between those two points, namely the EGC and the neutral.
    That puts normal-use current on the EGC, possibly even more than flows on the neutral wire, which is what the NEC specifically forbids. It risks elevating supposedly grounded metal to as much as 1/2 of the service voltage during a fault condition and can also interfere with proper operation of GFCI breakers in the main panel.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: Ground wire from PV to Controller

    Don't disagree about the current flow issues.

    Ideally, I would be suggesting 1:1 or X:1 isolation transformers--Then you can ground bond the neutral at the secondary output of the transformer--But that is not cheap and can be a bit of a power waste.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Ground wire from PV to Controller

    Thanks everyone, I'm SO sorry to have to bring up this discussion/fight again :) I know it is one of the most highly debated things here (and in the electrical world). I read thru HOURS of previous posts on grounding here and was still confused which is why I brought up my specific situation again here. And I do thank everyone for their input and I value it.

    So from what everyone is saying, I now understand lightning is the last of my concerns (that I have much control over) "grounding-wise" even though I am in the lightning capital (Orlando Florida area). And since my layout is PV --> Power House --> Main House then I believe I will likely in a better situation than most where their PV is ON the house. So it sounds like having a ground rod AT the PV will not hurt anything. Additionally, I will have the "main/Proper" ground rod at my "service" (the powerhouse) where my NG will be bonded.

    Question: Should I connect the two ground RODS together with a #6 bare and can I have that bare just direct buried or should it go in the PVC pipe underground?

    Then from the powerhouse, I will bring 4 conductors (2 hot, 1 neutral and one ground) to my main house panel WITHOUT the NG bond screw in it at the house panel. I will NOT have a ground rod there. Now I will ask the same question about this run as I did above: Can this bare #6 be direct buried or should it be in the PVC pipe? (From what I hope I just learned, I am leaning towards being in the pipe so it in itself does not become a long underground ground-rod right?).

    Thanks again, and sorry to cause a "debate".
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Ground wire from PV to Controller

    So far so mostly good.

    The NEC requires that the ground rod at the PV array, a ground rod if any at the power house and a ground system at the main house must all be connected together by wire. In NEC terms, your powerhouse contents do not make a "service" they make a "separately derived system". Not much difference except that for a service POCO can run just hots and a neutral to the first structure (where the fused disconnect or other OCPD is located) and then you have to run two hots a neutral and a ground to all of the other structures.
    Each structure must have its own grounding system, whether rod or pipe or plate or ring of Concrete Encased Electrode (CEE), and they must all be bonded together.

    Under NEC 2008 and later the bond between neutral and grounding system must be in only one location, as close as possible to the power source (i.e. at the powerhouse.)
    You are correct that you need to leave out the bond screw at the main house panel and you must connect both the in-house ground wiring and the local ground rod and the grounding conductor from the powerhouse to the ground bar in that panel. The neutral bar in that panel will be insulated from ground.
    SMA SB 3000, old BP panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Ground wire from PV to Controller
    inetdog wrote: »
    Under NEC 2008 and later the bond between neutral and grounding system must be in only one location, as close as possible to the power source (i.e. at the powerhouse.)

    In my opinion this is a mistake. The N-G bond should be as close as possible to the ground rod. In most utility installs (which are the basis of the majority of NEC including derivations applied to solar) this is the same thing.

    But then these are the people who think AC GFCI can be applied to DC in the same manner, and loose, rattling metal conduit is good enough for a ground path. :roll: Or at least at some point they did: nothing like the repeated waffling of regs to instill the fear of good engineering, eh?
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Ground wire from PV to Controller
    In my opinion this is a mistake. The N-G bond should be as close as possible to the ground rod.
    Ah, but which ground rod?
    I am guessing you would like to see the bond at the ground system for the main house instead of the ground system of the generator house?
    Definitely not at the array ground rod, we agree on that. :)

    Either way, there needs to be a four wire (including ground) feed between the power house and the main house, since that run is not a service and cannot use the POCO standard of running only a grounded (multiply grounded) neutral.
    SMA SB 3000, old BP panels.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Ground wire from PV to Controller
    inetdog wrote: »
    Either way, there needs to be a four wire (including ground) feed between the power house and the main house, since that run is not a service and cannot use the POCO standard of running only a grounded (multiply grounded) neutral.

    OK, but can the #6 bare ground be direct buried or does it have to go in pipe? Reason I ask is that I already have direct burial 2/2/4 AL feeding the house. Now I need to add a ground wire between. Wondering if I could just direct bury the #6 bare or should I run it in a pvc pipe (which would be new pipe run, but not a huge deal cause I have a trencher and a crap load of 1/2" pvc pipe laying around - but I'm not interested in doing more work than necessary :)
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Ground wire from PV to Controller
    jcheil wrote: »
    OK, but can the #6 bare ground be direct buried or does it have to go in pipe? Reason I ask is that I already have direct burial 2/2/4 AL feeding the house. Now I need to add a ground wire between. Wondering if I could just direct bury the #6 bare or should I run it in a pvc pipe (which would be new pipe run, but not a huge deal cause I have a trencher and a crap load of 1/2" pvc pipe laying around - but I'm not interested in doing more work than necessary :)
    I would be OK with making the #6 ground (EGC) wire an insulated wire (or single conductor cable) rated for direct burial. Or put it in a pipe. I would worry about corrosion in the damp soil if you use bare wire.
    There is nothing in the NEC that says that an EGC needs to be bare wire.
    Ideally, if insulated it should be green or green with yellow stripe, but I think that if it is single conductor cable the color does not matter.
    The bigger problem is that the EGC needs to run with (not just near) the other three conductors.
    I am also a bit concerned whether you meet the formal requirements for using a reduced size (#4) neutral. What is the amperage you will be running?
    If you have gone to bigger wire than necessary for amperage because you want to reduce the voltage drop, then you are required to up the size of the EGC from the calculated size by the same proportion. This will be an EGC (normally never smaller than the hot conductors) not a GEC (Ground Electrode Conductor) which can be smaller depending on the electrode type.
    Have you consulted with a local electrician about any of this wiring?
    SMA SB 3000, old BP panels.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Ground wire from PV to Controller
    inetdog wrote: »
    I am also a bit concerned whether you meet the formal requirements for using a reduced size (#4) neutral. What is the amperage you will be running?

    I got the wire for free, that is the only reason I am using it. I know it is oversized. It is about 120' (tops) from the powerhouse to the main House and I am only running (2) VFX3648 inverters and/or the Honda EU7000i generator so there is no chance I am ever going to push over 60 amps thru it; which is the size of the output breaker on the bypass breaker assy in the FW500Ac enclosure. Plus there is only a 50 amp breaker at the main house panel anyways so there would never be more than 50amps coming thru it.

    As far as consulting anyone. My dad is an electrical engineer and several friends work for the power company and another is a licensed electrician. Problem is, like we are finding out here, the engineer has their way of doing things and knows the theory behind everything, the power company people do things a totally different way because they are provind "service" (as discussed above), and the licensed electrician friend has no experience with PV solar (even though technically that should not matter) and that scares him off sometimes. Add "Grounding" to the mix and you can't get any 2 out of the 4 to agree on anything :)

    Also, I am way-way-off-grid. Like no code, inspections, police, fire or even roads, etc.
    I joke that my "driveway" is 7 miles long but you DO need a 4x4 to get here :)
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Ground wire from PV to Controller
    jcheil wrote: »
    I got the wire for free, that is the only reason I am using it. I know it is oversized. It is about 120' (tops) from the powerhouse to the main House and I am only running (2) VFX3648 inverters and/or the Honda EU7000i generator so there is no chance I am ever going to push over 60 amps thru it; which is the size of the output breaker on the bypass breaker assy in the FW500Ac enclosure. Plus there is only a 50 amp breaker at the main house panel anyways so there would never be more than 50amps coming thru it.

    As far as consulting anyone. My dad is an electrical engineer and several friends work for the power company and another is a licensed electrician. Problem is, like we are finding out here, the engineer has their way of doing things and knows the theory behind everything, the power company people do things a totally different way because they are provind "service" (as discussed above), and the licensed electrician friend has no experience with PV solar (even though technically that should not matter) and that scares him off sometimes. Add "Grounding" to the mix and you can't get any 2 out of the 4 to agree on anything :)

    Also, I am way-way-off-grid. Like no code, inspections, police, fire or even roads, etc.
    I joke that my "driveway" is 7 miles long but you DO need a 4x4 to get here :)

    OK, all code technicalities aside, when you use #2 for the hot wires, you really need to use #2 for the EGC too, otherwise the voltage divider effect can put exposed metal which is supposed to be grounded at a voltage close to 120V until the circuit breaker blows. (That is for an unlimited current supply, of course.) If your only source of AC is your PV, or a generator which cannot put out more than 200A or so, then you may be able to get away with a #6 EGC, but it would be, IMHO, still be a bad idea.

    Aside: the reason that the POCO does not have to follow the NEC is that they are under the National Electrical Safety Code (NESC) which puts a lot more emphasis on engineering to meet performance standards than do the cookbook rules in the NEC.
    SMA SB 3000, old BP panels.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Ground wire from PV to Controller
    inetdog wrote: »
    OK, all code technicalities aside, when you use #2 for the hot wires, you really need to use #2 for the EGC too, otherwise the voltage divider effect can put exposed metal which is supposed to be grounded at a voltage close to 120V until the circuit breaker blows. (That is for an unlimited current supply, of course.) If your only source of AC is your PV, or a generator which cannot put out more than 200A or so, then you may be able to get away with a #6 EGC, but it would be, IMHO, still be a bad idea.

    Well, that 2/2/4 wire is already buried (has been for some time). I could run another direct bury #4 AL as the EGC. I have plenty of extra of that (the 3rd extra piece, I use the 2 primary #2 wires for my PV to controller connection [way oversized I know] so I have the 2 "extra" #4's from those coiled up in my shop.)
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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