Author Topic: Grounding solar panels and ground faults. Any tie in to the charge controller?  (Read 656 times)

5 Minutes 2 Midnite

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I did a forum search on "grounding solar panels" and got no hits. Thus this post.

Was watching a youtube video on protecting a solar panel array from ground faults. When I did my system I paid close attention to grounding for lightening protection, but gave no focus to ground faults. The point of the video was that if any of the insulation were to rub off the wires of the solar panel wiring it should be detected as a ground fault. The reason given was reduced power and/or fire hazard.

My solar panels are grounded. I used weebs and bare copper ground wire connecting all the panels to a ground rod driven in about six feet from the panels.

My Classic 150 is grounded as per the manual. The ground wire goes to a different ground rod driven in just outside the building housing the CC and all the other equipment. The inverter is grounded to the same ground rod.

I kept earth grounding points to a minimum, based upon the best "best practices" strategies I could glean from reading about lightening protection (which should be a college level course based upon its complexity. Or perhaps a course in voodoo). Still I have TWO earth ground points. One at the panels. One at the equipment room.

QUESTION: Would the charge controller pick up a ground fault in the panel wiring?


« Last Edit: August 01, 2020, 04:03:24 PM by 5 Minutes 2 Midnite »
Qty 24 Sharp 153W poly panels, Midnite MNPV6 combiner, Midnite Classic 150 charge controller, Magnum MS-4448-PAE inverter with RC50 remote, Magnum MMP Mini panel,  QTY 2 Chinese made self-contained 200 AH wall mounted LFP power banks with built in BMS

ClassicCrazy

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I don't know the answer to your ground fault question but from what I have read on grounding - you want to tie them all together so everything is at the same potential.

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

ClassicCrazy

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Also not sure how you did the search - but to search every forum topic you need to go to the main forum page or else you won't get results.

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

Vic

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Regarding Ground Faults,  please read ALL that BB Bill has to say,  in the following  Thread:
http://midniteftp.com/forum/index.php?topic=142.0

Others have meaningful comments,  as well.  Bill is a very,  very sharp retired EE,   and has been the Super Moderator on the Wind-Sun Forum  for about a  decade.

Agree with Larry,  that the PVs should have a direct connection to ground,  outside any structures,   and  a connection twix the main system Ground and the PV module grounds   ...   generally.

Always hate to comment on other's ground questions,   as there are many variables that are very site and system-specific.

FWIW,   Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

5 Minutes 2 Midnite

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Thank you gentlemen. I have always threatened to string another length of copper between those two points. Your comments have prompted me to do so now.

I will keep searching on the question of if a ground fault on the panel wiring would be detected by the Classic, or to put it another way; how best to detect a ground fault on the panel wiring. But If anyone seeing this thread has an opinion please chime in.

Qty 24 Sharp 153W poly panels, Midnite MNPV6 combiner, Midnite Classic 150 charge controller, Magnum MS-4448-PAE inverter with RC50 remote, Magnum MMP Mini panel,  QTY 2 Chinese made self-contained 200 AH wall mounted LFP power banks with built in BMS

5 Minutes 2 Midnite

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I may have answered my own question. It appears from the wording in the Classic manual that any fault in the DC circuit will be picked up by the "Classic's internal GPF device".



The instructions are quite clear that nothing other than the ground point on the controller case should be grounded. This makes sense, as it lets the controller's GPF monitor the DC voltage in reference to ground.


The one thing I'm NOT sure of is what the voltage is if you check from positive to ground, and from negative to ground at the panels. In checking with my meter at the combiner, I get no PV voltage when measuring from negative to ground, but I get full PV voltage going from positive to ground. Is that normal? My guess it is normal. I assume ground is achieved through the GPF device. I guess its best not to think of this device like one would a circuit breaker. It's just a monitoring circuit.

Thoughts any one? Is PV voltage from positive to ground normal at the combiner?




The only thing connected to the grounding bar in the combiner is the lightening arrestor to the grounding rod.
« Last Edit: August 01, 2020, 09:16:05 PM by 5 Minutes 2 Midnite »
Qty 24 Sharp 153W poly panels, Midnite MNPV6 combiner, Midnite Classic 150 charge controller, Magnum MS-4448-PAE inverter with RC50 remote, Magnum MMP Mini panel,  QTY 2 Chinese made self-contained 200 AH wall mounted LFP power banks with built in BMS

Kent0

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The Midnite Classic has a PTC resistive device that is supposed to be the only connection between the PV- (also Batt-) and ground, otherwise it doesn't sense anything when there is a ground fault. Under normal circumstances the PTC is a low resistance to ground so you should measure 0.0 volts between PV- and ground and the full array voltage between PV+ and ground.

The instructions in the Midnite manual are not saying to ground the frames of the PV array to a separate ground. That is a code violation.  There should always be an equipment ground wire running with the PV wires, in the same conduit or cable (2020 NEC 690.45). The ground wire should be sized per 2020 NEC 250.122 based on the size of the breaker protecting the wire, or if there is no breaker protecting the wire, sized as if the breaker is 156% of the array's short circuit current.

For lightning protection, it is best practice for the separate grounds at the PV array and the charge controller to be connected together with a buried ground cable, but code does not require that. Many will point out that means having two ground wires connected to the two separated grounds - this absolutely does not cause a problem! - the buried ground wire bonds the two separate grounds into a single ground system.

5 Minutes 2 Midnite

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Thank you for replying Kent0

The Midnite Classic has a PTC resistive device that is supposed to be the only connection between the PV- (also Batt-) and ground, otherwise it doesn't sense anything when there is a ground fault. Under normal circumstances the PTC is a low resistance to ground so you should measure 0.0 volts between PV- and ground and the full array voltage between PV+ and ground.

Understood. No PV- wire or Batt- wire is grounded, and my voltage readings match what you specifiy.

The instructions in the Midnite manual are not saying to ground the frames of the PV array to a separate ground. That is a code violation.  There should always be an equipment ground wire running with the PV wires, in the same conduit or cable (2020 NEC 690.45). The ground wire should be sized per 2020 NEC 250.122 based on the size of the breaker protecting the wire, or if there is no breaker protecting the wire, sized as if the breaker is 156% of the array's short circuit current.

Understood. But I did not run a ground wire through the conduit. So for the moment let's back burner that as out of code.

For lightning protection, it is best practice for the separate grounds at the PV array and the charge controller to be connected together with a buried ground cable, but code does not require that. Many will point out that means having two ground wires connected to the two separated grounds - this absolutely does not cause a problem! - the buried ground wire bonds the two separate grounds into a single ground system.

This is where I am getting a bit lost. You reference "the separate grounds at the PV array and the charge controller". That statement seems to not be in alignment with running the ground wire through the conduit with the PV wire, because I am assuming that that ground wire connects to the same ground as the other equipment in the equipment room.

But it depends on if the solar panels are considered "equipment", if you know what I mean. As you can see in below photograph, the panels are grounded to a ground rod local to the array (6 gauge). The lightening arrestor mounted on the side of the Midnite combiner is also grounded to the same ground rod. I will be connecting this ground rod to the only other ground rod -which grounds all the equipment in the equipment room- 30' away, as you referenced above.

So, still setting aside any strict code violations, is this a workable configuration, both from the standpoint of lightening protection, and safety in terms of the Classic picking up any ground faults (insulation rubbed off a PV wire, etc.)?

« Last Edit: August 02, 2020, 02:27:57 PM by 5 Minutes 2 Midnite »
Qty 24 Sharp 153W poly panels, Midnite MNPV6 combiner, Midnite Classic 150 charge controller, Magnum MS-4448-PAE inverter with RC50 remote, Magnum MMP Mini panel,  QTY 2 Chinese made self-contained 200 AH wall mounted LFP power banks with built in BMS

Kent0

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It looks like your charge controller and batteries are not located at the PV array, so wherever the charge controller is located there should be grounding electrode. Your PV arrays are separate structures and should also have grounding electrodes. That is a different issue from having a properly sized equipment grounding wire in every conduit or cable assembly.

The conducting frames of every item in your system are considered "equipment" and are all to be connected together with equipment grounding wires. That includes the charge controller, combiner box, PV modules ... All made to be the same potential as earth by the grounding electrodes.

No, you cannot be confident that the Classic will detect a ground fault unless there is a ground wire in common between the location of the Classic and the location of the PV array.

Thanks for sharing the photo. By the way, all the wires over 30 volts are supposed to be guarded by putting them in conduits, behind barriers, or out of reach. Please consider getting help from a local professional.


5 Minutes 2 Midnite

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Thank you for sharing your experience. I will consider the question posed in this thread as having been fully addressed (not to inhibit anyone else from chiming in however).

Having said that, if you care to, as in, if you enjoy discussing this general topic of grounding, and are not burned out from however many threads cover the topic... I am curious about a couple of things. Otherwise, thank you again for your time!

The conducting frames of every item in your system are considered "equipment" and are all to be connected together with equipment grounding wires. That includes the charge controller, combiner box, PV modules ... All made to be the same potential as earth by the grounding electrodes.

Emphasis mine. I really like that last sentence. It seems to me that if there is one way to summarize this topic, it is that statement, "... All made to be the same potential as earth by the grounding electrodes." Like no matter how weird or confusing it gets, simply refer back to that sentence. Get everything to the same potential. Then unwanted current flows are mitigated.

It looks like your charge controller and batteries are not located at the PV array, so wherever the charge controller is located there should be grounding electrode. Your PV arrays are separate structures and should also have grounding electrodes. That is a different issue from having a properly sized equipment grounding wire in every conduit or cable assembly.

OK. Regarding that last sentence... having the ground wire inside the conduit, or put another way, having the ground wire adjacent to any cabling... is there an overriding reason that the wire be inside, not outside? For example in my case the current plan, as I was mentioning, is to run a ground wire between the two grounding electrodes (panel grounding electrode to equipment grounding electrode). Strictly in terms of the grounding configuration (what's connected to what), I am assuming that I will achieve a similar effect as if a ground wire had been run from the combiner, through the conduit, into the equipment room, and then terminating at the same grounding electrode all the other equipment is bonded to. I am further assuming that then I can then be confident that the Classic will detect a ground fault.

So the question is, what is gained by running the ground wire through the conduit? This is assuming the the external wire I will be running is buried and therefore the wire is protected in both cases? Let me try to answer my own question before anyone else does. Is it a question of exposing the ground wire to the earthen ground when it is run externally? Meaning, that by running the wire inside the conduit you are preventing any spurious potentials and current flows? Thus, having the wire inside you are being more deterministic in controlling precisely what the ground wire will achieve.... that being getting everyone to the same potential. ??


By the way, all the wires over 30 volts are supposed to be guarded by putting them in conduits, behind barriers, or out of reach. Please consider getting help from a local professional.

You will notice that the rear array is pretty much free of any exposed wires. That array was installed after the one in front. I'm learning from my mistakes as I go. One of the reasons I've been posting so many queries is that now that the system is complete (3-years in the making), I'm now going back to identify and correct my mistakes. ;>
« Last Edit: August 02, 2020, 06:01:32 PM by 5 Minutes 2 Midnite »
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boB

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I think that Kent meant the PV + and - wires going through the conduit ?   (Hi Kent !!! )

The ground wires are, by definition  (I think) at ground potential and not more than 30 V ?

So he may have been talking about the black and red wires more in the middle of the PV array to the combiner box on top of that pole ?

K7IQ

Kent0

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Generally there is a code requirement to run an equipment ground with conductors, sizing that equipment ground for PV wiring is what 2020 NEC 690.45 is addressing. So with the exception of the exposed wiring behind the PV modules, there should be an equipment ground running with the conduit or cable with the PV wiring. For DC circuits, the equipment ground is usually allowed to be outside the conduit, or to be run separately; but you still have to have one. A home run from the house or power shed to the PV array with just PV+ and PV- wires is not correct. It is part of the scheme in the code to keep everything, other than the conductors, at the same ground potential.

5 Minutes 2 Midnite

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Very well. Thank you.
Qty 24 Sharp 153W poly panels, Midnite MNPV6 combiner, Midnite Classic 150 charge controller, Magnum MS-4448-PAE inverter with RC50 remote, Magnum MMP Mini panel,  QTY 2 Chinese made self-contained 200 AH wall mounted LFP power banks with built in BMS