PV Grounding & Wiring to Inverter

[Roadking66]

Trying to get clarification on grounding and wiring due to lots of conflicting information and confusion regarding grounding of solar systems. I have two ten panel (560v each) arrays I need to wire to my utility shed that houses my EG4 18KPV inverter and EG4 Power Pro batteries located about 80 feet from my arrays. From there I need to wire my inverter to the AC disconnect at the house about 70 feet from the utility shed. The AC disconnect will get wired to the house. The house will be earth grounded with two 8 foot ground rods 8 feet apart. Initially I was told I needed to earth ground the panels, then run that ground along with the PV wires to the inverter. I was thinking that would create the dreaded ground loop? I called Signature Solar and was told that the PV arrays do get earth grounded, but no further, and not to run that ground to the inverter. The inverter get grounded when I run the positive, negative, and neutral Load from the inverter to the AC disconnect. Then onto the house main panel which is earth grounded to two 8 foot ground rods 8 feet apart. I always like to trust but verify what I was told. Was I told correctly not to run ground from the panels to the inverter?

 

[robbob2112]

Summary - there can be only one ground - in your case the twin rods at your house.

The wires to the house will have a ground I assume you are using something like SER cable - 4 wires total - 2 hots, a neutral, and a ground wire. Pure copper - if you do aluminum you will need to upsize quite a bit and make sure where you connect is rated for AL at both ends.

The wire from the house is connected in your panel there and there is a neutral-ground bond screw there.

At the shed end you tie that ground wire to the equipment grounds for all the boxes, raceways, conduit, etc ....but no ground rod.

From the MPPT/AIO in the shed you run 3 wires out to the PV panels - the pos and neg and the EGC. The Equipment Ground Conductor is tied to the racking if metal, the panel frames, any combiner box ground. but no ground rod

NOTE - you can use one EGC for multiple sets of pv current carrying wires. Here is a link to the table from the NEC. The rules can get a little complicated but you size it for the expected current in case there is a fault. This means if you have just a pair of 10awg wires your max size would be 10awg. If you have 2 pairs of 10awg wires your max is still 10awg. This is because the max fault at a time is expected to be just one set of wires.

another note - at no point do you tie the PV current carrying wires or the battery wires to ground. You also don't connect pv negative to battery negative on your own. Non-isolated MPPT will do it for you and for the isolated MPPT you don't want to or you can damage it...

Generally you can go down one size and be ok, but consult the local AHJ and follow it ... usually they just say to use the NEC table.

Post in thread 'Robbob2112 Answer thread'

Dec 1, 2024

Just because I can never find the chart for the EGC size when I need it, adding it to my answers



NEC Table 250.122 specifies the minimum sizes for equipment grounding conductors (EGCs) based on the rating of the overcurrent protection device (OCPD) safeguarding the circuit. Proper sizing of EGCs is crucial to ensure a low-impedance path for fault currents, facilitating the prompt operation of protective devices and enhancing safety.

**Using NEC Table 250.122:**

1. **Identify the OCPD Rating:** Determine the ampere rating or setting of the OCPD (e.g., circuit breaker or...

• robbob2112

• 

At the array you do not drive a separate ground rod.... If you are using metal racking then you can't help it and that is know in the NEC as an auxiliary ground and doesn't count.

At the array you will want a good DC SPD per set of PV cables. At the shed you will want a good DC SPD per set of PV cables. At the house and shed end of the AC wires you will want a good AC SPD.

For the wires between the shed and the array - they get sized based on expected current carried from the PV panels multiplied by 156% ... odd number... if your panels generate 10amp, the wire size must carry 10amp * 1.25 * 1.25 = 15.625amps -- this way no matter what short happens they wires don't get hot. If you put them in conduit with more than 3 current carrying wires you derate to 80% of what they will carry. The EGC is not a current carrying wire, but does count for fill when you figure your conduit size.

 

[timselectric]

Was I told correctly not to run ground from the panels to the inverter?

No
All grounding ties together to become the grounding system.
The grounding system begins at, and is created by the N/G bond.
Everywhere you run circuit conductors, you also run an EGC (Equipment Grounding Conductor) along with them. All EGC's are connected together and bonded to all metal enclosures, raceways, and grounding terminals of equipment. You only want to connect the earth to your grounding system at one location. (Your two ground rods 8ft apart)

 

[Roadking66]

OK…let me know if I understand this correctly. The panels in each separate array are bonded together. From there each array utilizes a ground wire along with the PV wire. The PV’s remain separate and go to their respective DC Disconnects, but the ground can be combined into one. Then the two PV sets along with the one combined ground run to the inverter in the shed. Then onto the AC disconnect at the house from the inverter via red, black, neutral. From there to the main sub panel which is then grounded to the earth ground rods 8’ deep, 8’ apart. There is no earth ground rod at the panels. I can/should utilize surge protection devices before the inverter. Three questions: if I combine the grounds from the panels and after I run the PV through their DC Disconnects, can I run all 5 wires through a gang box, basically combining this ground with the two sets of PV wires into a single conduit? If I run them separate should I just not combine the grounds and run three wires each through smaller conduit? Two conduit runs in the same trench? Seems like more work and cost? Is the ground used in this case bare or coated? Would the surge protector of choice be the EMP Shield device I’ve seen in several videos? Thank you for the advice and I’m learning more with every post.

 

[robbob2112]

You can run the pv wires from both arrays are the egc through the same conduit to the array, but 4 current carrying wires means you derate their capacity to 80%.

All of your ground/egc wires will combine in the shed so they ultimately connect all the equipment shells together and back to your house ground.

If you choose to run the pv wires in separate conduit, i.e. they run to different locations, there needs to be a separate egc in each conduit.

The ac cable will be red, black, neutral, ground.

I personally like the midnite solar SPD.

 

[Roadking66]

Ok…so best practice here would be to keep the two PV runs separate to the shed. Bond the panels together (they are on Powerfield PowerRacks not metal racks). No earth round rod. Each in their own conduit, two current carrying wires and one equipment carrying ground each. All 10awg. Is the ground bare copper or coated? Thanks!

 

[timselectric]

Is the ground bare copper or coated?

Either is code compliant.
I never use bare copper for anything.

 

[TM48]

AC disconnect at the house from the inverter via red, black, neutral. From there to the main sub panel which is then grounded to the earth ground rods 8’ deep, 8’ apart.

You must have an EGC between the shed and what you call the main sub panel. And also if you are subject to building codes you will have to comply with the inspector who may insist you drive a ground rod at the array. (mine did)

 

[Roadking66]

You must have an EGC between the shed and what you call the main sub panel. And also if you are subject to building codes you will have to comply with the inspector who may insist you drive a ground rod at the array. (mine did)

Yes…there will be an EGC along with the three Load wires going from the inverter in the shed to the AC Disconnect, then onto the main panel. The main is already grounded to the two ground rods 8’ apart. I guess the only variable remaining is weather I need a ground rod at the arrays. Consensus here is no, but you’re saying an inspector might require one…

 

[TM48]

Yes…there will be an EGC along with the three Load wires going from the inverter in the shed to the AC Disconnect, then onto the main panel. The main is already grounded to the two ground rods 8’ apart. I guess the only variable remaining is weather I need a ground rod at the arrays. Consensus here is no, but you’re saying an inspector might require one…

If you're subject to inspect I highly recommend you pay them a visit before you buy anything.

 

[Roadking66]

If you're subject to inspect I highly recommend you pay them a visit before you buy anything.

AHJ will review everything before permit is issued. I’m just trying to improve my knowledge base and clean up the design to submit to my engineer. Then their planset will go onto the AHJ.

 

[hwy17]

I would use 1 conduit, 3/4" PVC if you don't think you will ever want to add more arrays at this location or maybe 1" if you might want to add more arrays later.

10 AWG stranded THHN: 2 Red, 2 Black, 1 Green.

There's some work to do on verifying the amperage and derating with the NEC. 1.56x ISC, multiple conductor derating, etc. but I'd be surprised if that's not legal.

I can't believe Signature is still telling people to not run a ground to remote arrays. That's only for when your chinese inverter is leaking AC and you have to protect yourself from it but those people should still want the ground in the conduit for when they get a safe inverter.