Ground rod for each array connected?

Hello folks, I have been doing more reading on PV grounding and am more confused now than I was before. I'm questioning my current existing grounding of my two pole mounted arrays.

Each pole mounted array is grounded with a proper lug on each panel with a single continuous wire thru every panel down to a ground rod for that array.

My question is, should I connect both ground rods together with an underground bare ground wire?

My system is 24 volt with grounded neutral (negative).
Should I even ground the negative since the system voltage is under 50 volts?

The system has been fine, but I'm still not sure how I should have this grounded.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Ground rod for each array connected?

    Here is a thread with lots of grounding discussions:

    http://forum.solar-electric.com/showthread.php?t=903

    And another post with grounding links:
    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.

    Towards the end of this thread is a very nice discussion of proper generator grounding.

    -Bill

    Basically, my guess would be to tie the two earth ground rods together... If there is a panel +/- to earth short at the array, the ground wire back to the battery shed ground rod will help prevent anything from getting energized and causing a shock or electrolysis of your steel and water pipes.

    But that does get back into the issue of grounding or not grounding the battery bank negative post... In general, I am a fan of ground bonding the negative battery post. It helps prevent problems of high current flowing in the DC Return wires (which do not usually have a breaker/fuse).

    But when you do the grounding, you have to be careful not to cause ground loops (say grounding the DC- at the array and again grounding the DC- at the battery terminal, both to earth ground.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Ground rod for each array connected?
    BB. wrote: »

    But when you do the grounding, you have to be careful not to cause ground loops (say grounding the DC- at the array and again grounding the DC- at the battery terminal, both to earth ground.

    -Bill
    You don't want to do that, anyway. Grounding the DC- at the array would defeat the GFI on the system.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Ground rod for each array connected?

    Actually, I believe the DC GFI is actually unsafe (both fire and electrocution) at the system level and provides only a little bit of Arc Fault protection--which it was originally designed for...

    http://midnitesolar.com/smf_forum/index.php?topic=142.0

    By the way, here is the original thread from the Wind-Sun forum:

    http://forum.solar-electric.com/showthread.php?t=10650

    However, my example was just more pointed to creating ground loops with distributed grounding/ground rods.

    If James' system has DC GFI installed/enabled--Yes it is not a simple yes/no question.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,380 ✭✭✭✭✭
    Re: Ground rod for each array connected?
    James wrote: »
    .... Each pole mounted array is grounded with a proper lug on each panel with a single continuous wire thru every panel down to a ground rod for that array.....

    Well, the pole, and all the metal bolted to it, is likely grounded, where it enters the ground. Concrete Encased Electrode (UFER) Grounds are pretty efficient.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Ground rod for each array connected?
    James wrote: »
    My question is, should I connect both ground rods together with an underground bare ground wire?

    This is something I would definitely not do. It creates the potential for a lower resistance pathway from one grounding point to another, and therefor raises the possibility of any current entering at one ground terminal to come back up at the other and energize something there, rather than have the current dissipated in the earth. This is the "ground loop" problem you've no doubt heard about.

    Note that this is not the same as when grounding connects to a single rod which then has lines leading out to additional rods. In that case there is no return from earth that would allow current to re-enter the system at a different point should the ground path prove high resistance.

    As Mike said, the pole mount itself is likely a good enough ground. Adding more ground paths is not better.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Ground rod for each array connected?

    james,
    i feel that joining them together is ok to do as it would just essentially be a better lightning ground, but if the distances between the arrays is large this can be difficult and expensive to do. my bigger concern would be just how up to date with the nec you might be as bill pointed out one aspect, but also in the respect of running a ground wire back into your home with the pvs wires is another. if you did not run a ground wire back into your home with the pv wires then i would be more inclined with those external underground array grounds being tied back to the main ground rod at either your utility service entrance or off grid main grounding rod. running one underground and one with the pv wires would be 2 paths to ground and should be avoided as that is what causes ground loops is multiple paths. if you do run the underground ground wire to the main ground rod at the home then also tie the 2 pole arrays together and it would form a triangle underground. like i said, if distances are too great then don't bother, but ideally they should be connected underground.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Ground rod for each array connected?
    James wrote: »
    My question is, should I connect both ground rods together with an underground bare ground wire?
    I would not, as stated above.
    Now as to the pole/mounts being a good ground. Will tend to the no side. This will very on mount construction and soil conditions.
    James wrote: »
    My system is 24 volt with grounded neutral (negative).
    Should I even ground the negative since the system voltage is under 50 volts?
    If using an ungrounded system. All disconnects must break BOTH conductors. Plus I think you must fuse both conductors. By going this way will just add $$$ to the project.
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Ground rod for each array connected?
    James wrote: »
    Hello folks, I have been doing more reading on PV grounding and am more confused now than I was before. I'm questioning my current existing grounding of my two pole mounted arrays.

    Each pole mounted array is grounded with a proper lug on each panel with a single continuous wire thru every panel down to a ground rod for that array.

    My question is, should I connect both ground rods together with an underground bare ground wire?

    My system is 24 volt with grounded neutral (negative).
    Should I even ground the negative since the system voltage is under 50 volts?

    The system has been fine, but I'm still not sure how I should have this grounded.

    Grounding the two arrays with a underground bare wire won't hurt if your utility ground system has a good bond to the arrays already and the utility ground point is a good quality low impedance connection to earth. If your utility ground is poor then the utility ground reference will shift to your array ground when a surge from the utility power lines or a near lightning strike happens. If this happens the ground wires from the arrays to the house can develop surge voltage spikes from the current flow and send them into the grounding wiring at the house possibly causing equipment damage.
    (EM field simplification of grounding) The engineering objective in grounding is to reduce the E (voltage) field to the lowest possible extent by maximizing the B (current) field. The local energy of very high current faults can be reduced to almost zero if the voltage is near zero because energy/power is the product of the fields E*B (voltage*current) By keeping the energy restrained in the B (current) field until it is safely carried into the ground with a low impedance copper rod, we move the E (voltage) field generation point near the bottom tip of the grounding rod.

    You best bang for buck is to make sure the house utility ground is good and use quality surge protectors connected to that ground on every wire or cable that enters the house.
  • JamesJames Solar Expert Posts: 246 ✭✭
    Re: Ground rod for each array connected?

    Thanks for the replies.
    The system does not have DC GFI installed and I do have a grounding conductor wired (in conduit) with the + and - conductors to the house. I should also mention my utility ground rod is at the opposite side of the house. I'm not net metering, but the inverter AC end is grounded to the utility ground thru the AC in grounding (inverter's charger used for backup)
    That in itself may present problems....I'm way confused...Does'nt that create a ground loop also? (PV system ground and AC system ground on different ground rods?

    Looks like I still don't know what's best....The John Wiles code corners don't seem to address the multiple array ground rod issue directly, and the replies here still leave me undecided.
    ???
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Ground rod for each array connected?

    If you have two grounding rods that are not bonded together outside of your house and enter at different points then the current path for a loop (voltage potential difference) will be inside your house wiring. There should be only ONE grounding point connection (usually the ground bar on the main service panel) for any rod ground wire that enters your house. (usually the utility ground) There will always be possible (external to your house) current loops with more than one grounding rod but as long as the power from that says outside and is shunted into the ground before entering the house it's fine for surge protection.

    http://ecmweb.com/mag/electric_hit_grounding_home/
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Ground rod for each array connected?

    with the ground lead coming into the house with the pv wires, i would do nothing more than you already have. a difference of potential can still occur as a result of the pv grounds and the main ground as soil resistance is not at 0 ohms. the potential difference will however be small due to this resistance. making the pvs tie together would essentially lower the resistance through the soil to the main ground and larger potential for ground loops will occur as a result.

    you are going with nec compliance and i can't recommend that you violate it, but i do not agree with the ground lead coming into the house with the pv leads as it is unnecessary and dangerous in my opinion. maybe as a result of mr wiles' blunder that if any property or lives become hurt or sacrificed as a result of his determination that he and the nec as well as any local governmental body be held liable for such. what they are doing there is contradictory to the purpose of what the nec and those governmental bodies were formed for as they are needlessly endangering lives and property.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,667 ✭✭✭✭✭
    Re: Ground rod for each array connected?
    nsaspook wrote: »
    If you have two grounding rods that are not bonded together outside of your house and enter at different points then the current path for a loop (voltage potential difference) will be inside your house wiring. There should be only ONE grounding point connection (usually the ground bar on the main service panel) for any rod ground wire that enters your house. (usually the utility ground) There will always be possible (external to your house) current loops with more than one grounding rod but as long as the power from that says outside and is shunted into the ground before entering the house it's fine for surge protection.

    http://ecmweb.com/mag/electric_hit_grounding_home/

    Nice link and good advice! Thanks!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • JamesJames Solar Expert Posts: 246 ✭✭
    Re: Ground rod for each array connected?

    My thanks to all, I'm starting to have a better understanding of this. I can see the differences between system grounds and the array framing ground.
    the link from nsaspook was also interesting and helpfull, thanks.

    I'm considering disconnecting the ground line from the combiner box to the home and keeping the PV array framing grounds going directly to the ground rod beneath each array. I would also keep the ground line from the combiner box ground lug to the ground rod as it is.

    Then I would keep the interior equipment grounds tied to the house ground system rod.

    What I'm not sure about with that set-up, is if I should tie the battery bank negative to the house ground also...???
  • JamesJames Solar Expert Posts: 246 ✭✭
    Re: Ground rod for each array connected?

    Hello, I think I've got a handle on the ground rod/array issue, but I'm still not sure what, if anything, I should do regarding the battery negative lead tied to ground issue? Any more thoughts on this? Thanks much.
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Ground rod for each array connected?

    I see no reason not to ground 12 and 24 volt system even if the PV voltages never tops 50 volts. It reduces the required fusing and disconnects to a single pole instead of two. Most devices have the negative connected to ground internally anyway and it might reduce EMI/RFI from the charge controller/inverters.
  • JamesJames Solar Expert Posts: 246 ✭✭
    Re: Ground rod for each array connected?

    thankyou for the perspective on this. sounds good to me
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