Author Topic: Grounding question  (Read 2248 times)

rubiks1

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Grounding question
« on: August 16, 2015, 02:00:11 PM »
Hello Everyone

Hope all is well with everyone. I have a grounding question today for everyone, it is a bit long winded so here goes.

System overview
Outback GVFX3524  inverter, FM60 charge controller with 3 strings of 2 235 watt panels. battery bank 8 concorde 3050t 6 volts for a total of 610 AH.
Also I have a 5.2 kw grid tie system that was installed by a local solar company in 2007 and when they installed the system they could not find any ground rod etc so they drive a 8 foot ground rod into the earth and attached the grid tie system to it and then they ran a bare #8 (will need to check) to the pipes of the house.

When  I installed the off grid system (a year before I knew anything about ac coupling) I drove a separate ground rod (other side of the house) and grounded my panels, combiner box, epanel that the outback inverter is mounted onto that ground rod. When I brought over my 40 amp ac circuit from my subpanel to feed the outback a ground came with it and I landed it onto the ground bar in the epanel which is also where the ground from the ground rod is landed.

So now that you know all of that here is the question. Is this grounding correct?
Also I live in N CA and we dont get thunderstorms etc

Thanks
Brad


zoneblue

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Re: Grounding question
« Reply #1 on: August 16, 2015, 04:25:05 PM »
Yeah yours is kinda complex setup. You have to be careful to follow local codes. But such codes rarely explicitly envisage systems with multiple power sources. Over the years of trying to digest our local codes, i try to aim to:
- ensure that everything that needs to be grounded is grounded
- try to centralise the grounds, and keep multiple stakes bonded together using the most direct and least corosion/damage prone method
- try not to create ground loops, this means keeping track of where each thing is grounded
- try not to bring lightning into the house

I know this isnt a direct answer, and probably the best solution for you is to get a sparky to look at it.  You could also try to read the NEC which is available online at https://archive.org/details/nfpa.nec.2014
6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

Kent0

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Re: Grounding question
« Reply #2 on: August 16, 2015, 04:51:33 PM »
In 2007, the installers should have either 1) installed two ground rods at least 6 feet apart or 2) provided documentation showing that the single ground rod was tested and has a resistance to remote earth of less than 25 ohms. The 2014 NEC specifies the installation of a supplementary ground electrode as close as possible to the roof mounted PV array. It sounds like that is consistent with the ground rod that you added. I wouldn't connect anything to that electrode except the PV array and I would also have another #6 copper ground running to the PV array from the original grounding system. Anything connected to the supplementary ground electrode creates a circumstance where you have two ground electrode systems that are connected together with the equipment ground wire that runs from the new system to the original system. When there are events, such as nearby lightning or geomagnetic storms, that cause the two grounding systems to have different potential, current will flow through the wiring between them. It is much better to have all the grounds in the house run to a single ground electrode system at one spot.
« Last Edit: August 16, 2015, 04:56:10 PM by Kent0 »

tecnodave

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Re: Grounding question
« Reply #3 on: August 17, 2015, 11:02:52 PM »
Brad,

Code here in n.cal is for a 6 ga. Ground wire from the primary power source directly to the ground rod with no splices and a secondary ground to the water pipes and gas pipes , this goes from the neutral buss in the main panel to the pipes. Any auxiliary ground rods are connect with one piece 6 ga. Wire to the main ground rod.   

You are close but if that is 8 ga. You are undersized. This is good up to a 200 amp main panel. Even a 30 amp 120 volt service will require the two grounds as specified above, not under 6 ga. In any circumstance.

Practicing commercial electrician in nor cal

td
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 2 Suntech 280 24v AGM 105 a.h. Exeltech Inv.
#4 Kid/WBjr 2 Suntech 280 12v AGM 105 a.h.

rubiks1

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Re: Grounding question
« Reply #4 on: August 18, 2015, 12:40:54 AM »
Thanks for all of the replies. I do appreciate it.

Technodave

The ground wire going to the offgrid panels to the ground rod that I installed is a #6 bare copper. Also the epanel is grounded to this rod with a #4 THHN insulated ground. Also my service is 100 amp. If I am reading you post correctly then to make it code compliant I would have to run a bare #6 from this ground rod to the other one on the other side of the house and connect it there? Can you also tell me about the ground that I am bring over from the 40 amp ac feed into the epanel since both the 40 amp ac feed and the new ground rod both land on the same ground bar, is this ok? If not how do I correct it?

Thanks

Brad

Brad,

Code here in n.cal is for a 6 ga. Ground wire from the primary power source directly to the ground rod with no splices and a secondary ground to the water pipes and gas pipes , this goes from the neutral buss in the main panel to the pipes. Any auxiliary ground rods are connect with one piece 6 ga. Wire to the main ground rod.   

You are close but if that is 8 ga. You are undersized. This is good up to a 200 amp main panel. Even a 30 amp 120 volt service will require the two grounds as specified above, not under 6 ga. In any circumstance.

Practicing commercial electrician in nor cal

td

tecnodave

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Re: Grounding question
« Reply #5 on: August 18, 2015, 01:40:21 AM »
Brad,

Your system is more complicated than that. First you can only connect neutral from PG&E to the grounding system at one point. That will be at the PG&E main box. The feed to the outback must be 3 wire service for a 120 volt service or a 4 wire service for 120/240 split phase. Neutral and ground cannot be connected anywhere else in the system unless you throw a transfer switch to shut off grid feed. If you house is newer maybe 70's and newer the grounding system used here is the
"Ufer ground" that is the rebar in the foundation being tied together and connected to the electrical box. The "Ufer ground " is far more effective than several ground rods but sometimes if hard to find the connection point. There should be a piece of rebar extending out of the slab or foundation near the main panel with a bolted clamp for the ground wire.

 The other area to address is the AC ground and DC ground. They need to be tied together with a wire no smaller than the smallest wire used in the DC system.

The best explanation of inverter grounding wiring that I have found is in Magnum's manual for the MSH-4024-RE and the MS-xxxx-PAE line. They spell out the three options. Download that manual, it will make things clear.

My own system is totally off grid but I do have PG&E with a standard ground rod. I have an array on the building that has the PG&E service. It has 4 ga grounding from the array to the DC ground rod and a 4 ga jumper to the PG&E ground. Array output goes under ground 166 feet to an R.V. Where the controllers, batteries and inverter are. There is a third ground rod here with quad ott (0000) cable from batt neg and motorhome frame to ground.

No we don't have thunderstorms here......if you don't look!   I've had 20 strikes too close for comfort. My next purchases will be midnite lighting surge protectors.

Hope this will help.   td
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 2 Suntech 280 24v AGM 105 a.h. Exeltech Inv.
#4 Kid/WBjr 2 Suntech 280 12v AGM 105 a.h.

rubiks1

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Re: Grounding question
« Reply #6 on: August 18, 2015, 02:35:57 AM »
Dave

I have a pic below. Looking at the ground bar, circled in red is the #4 thhn insulated ground wire from the new ground rod I installed.  The second #4 thhn is the ground for the inverter. Circled in black is a #8 wire that is coming in from my sub panel. That is the 40 amp feed for the ac in.  Please tell me if this is correct. I need to remove this epanel from the new ground rod and use the ground from the 40 amp feed coming over?

As far a the neutral ground bonding that is only done at the main panel where the meter is. It is not done at my subpanel or in this epanel. When the grid tie system was installed we looked for that ufer and could not find it so the electrician decided to install a ground rod and then he ran a wire from there to the pipes.




Thanks again.

Brad

tecnodave

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Re: Grounding question
« Reply #7 on: August 18, 2015, 01:27:07 PM »
Brad,

That looks ok, just be sure green and white are separated here, it's ok to have an additional ground rod , that additional rod connects back to the main ground buss in the main panel just as you have it.

I think that because this ground wire is not only the AC feed for the inverter/charger but also the bonding wire that connects the two ground rods togather that it must be insulated 6 ga. copper at the smallest.   The hot and neutral can be 8 ga. as the inverter is 40 amp service.

Your electrician did right.....if you cannot verify the existence of a valid ground be sure you make one.
I have pulled out the corroded stubs of old ground rods that appeared ok on the surface on many more than one instance

td
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 2 Suntech 280 24v AGM 105 a.h. Exeltech Inv.
#4 Kid/WBjr 2 Suntech 280 12v AGM 105 a.h.

rubiks1

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Re: Grounding question
« Reply #8 on: August 18, 2015, 06:39:38 PM »
Yep green and white are separated. As far as wire size you are correct that is a 8ga for the hot, neutral, and ground not a #6.  Since I currently have this system and a 5.2kw grid tie and the plan is to merge the two together (entire new thread) I will most likely hold off on this until this.

Thanks for all of the help. I do appreciate it.

Brad

Brad,

That looks ok, just be sure green and white are separated here, it's ok to have an additional ground rod , that additional rod connects back to the main ground buss in the main panel just as you have it.

I think that because this ground wire is not only the AC feed for the inverter/charger but also the bonding wire that connects the two ground rods togather that it must be insulated 6 ga. copper at the smallest.   The hot and neutral can be 8 ga. as the inverter is 40 amp service.

Your electrician did right.....if you cannot verify the existence of a valid ground be sure you make one.
I have pulled out the corroded stubs of old ground rods that appeared ok on the surface on many more than one instance

td

zoneblue

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Re: Grounding question
« Reply #9 on: August 19, 2015, 04:25:47 AM »
The best explanation of inverter grounding wiring that I have found is in Magnum's manual for the MSH-4024-RE and the MS-xxxx-PAE line. They spell out the three options.

Well from that manual their option 3 is what i use. However it does not meet code HERE, because the AC GEC is not not permanently spliced at the DC ground bus. I still think its a good option because it reduces the corosion issues somewhat.

6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
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rubiks1

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Re: Grounding question
« Reply #10 on: August 21, 2015, 06:30:14 PM »
So other than the 8ga ground not being a 6 ga or better all is good? No need to unhook the epanel from the additional ground rod etc?

Thanks
Brad



Brad,

That looks ok, just be sure green and white are separated here, it's ok to have an additional ground rod , that additional rod connects back to the main ground buss in the main panel just as you have it.

I think that because this ground wire is not only the AC feed for the inverter/charger but also the bonding wire that connects the two ground rods togather that it must be insulated 6 ga. copper at the smallest.   The hot and neutral can be 8 ga. as the inverter is 40 amp service.

Your electrician did right.....if you cannot verify the existence of a valid ground be sure you make one.
I have pulled out the corroded stubs of old ground rods that appeared ok on the surface on many more than one instance

td

Powerplay

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Re: Grounding question
« Reply #11 on: February 09, 2016, 10:41:37 AM »
Zoneblue:  Just to test if I understand your diagram, I'm thinking of something similar when I plan to add a MagnaSine inverter to my off-grid system.  I have the twin 8 foot ground rod set up for my dedicated DC system ground.  Would this diagram present issues if AC power from the house mains was brought in to the AC-in terminals and AC ground connected to the second AC ground terminal in the MagnaSign inverter.  If I'm thinking correctly, this presents two separate AC neutral to ground bonding scenario, the other at the house main panel, that would be a no-no.  Also, I'm unsure how internal Classic GFI circuit plays here.  My Air Conditioner zone, powered entirely by off grid power will be wired by 14/3 wire and I'll likely need an Air Conditioner disconnect that does not bond neutral to ground.

Am I seeing things correctly here?  Thank you.
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%

zoneblue

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Re: Grounding question
« Reply #12 on: February 09, 2016, 04:40:58 PM »
I attempted to clarify my thinking on teh subject here:
http://zoneblue.org/cms/page.php?view=system-earthing

Its a bit tricky because the NEC and other codes like it all look rather to be AC grid service centric, and the DC (or other seperately derived systems) appear added as an afterthought. Hence the jist of what they envisage is one AC to neutral bond located at the point where the ground bus connects to the GEC + GE.

So when we have a DC negative to ground bond as well, and sometimes a seperate DC ground bus, then, obviously everything needs to be linked togther, but the fine points of that is where it gets tricky, what with all teh language about permanently spliced and what not. Personally i dont think it matters where the GEC is connected (DC or AC), so long as its all really tight. I mean which is more dangerous 100 and something AC or 100 and something DC.

If you come to any better conclusion feel free to chip in.
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Powerplay

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Re: Grounding question
« Reply #13 on: February 09, 2016, 08:24:41 PM »
No other notions, I liked your diagram and I'm just mulling it over.  I think for my next stage, I'll leave the house's main panel out of it and install an AC service panel and DC distribution panel beside the inverter(s) with correct breakers and wiring and follow the style of your diagram.  Then I'll have an interesting discussion with the HVAC guy about whether there are any L1-N circuits in the HVAC (mini split zone) or are they all L1-L2.  Now I just need to find some green colored insulated number 6 wire sold by the foot.

Thank you for the reply.
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%

Powerplay

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Re: Grounding question
« Reply #14 on: March 30, 2016, 02:06:21 PM »
@ Zoneblue: I modified a version of your (ver. of Magnum's #3) grounding diagram to wire my new power center.  It worked like a champ from the get go.  I was even able to find all the correct wire colors and gauges to make things look snazzy (to my eye anyway) in there.  Thank you for getting me started with the post.
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%