Multiple ground rod

[sumya]

Hello,

See attached picture for my system. My question is, for this off-grid system, is it okay to have two separate grounding rods which are 51 feet away? OR do I need to connect my solar panels to the inverter with a ground bare copper wire?

Thank you.

 

[rhino]

No matter what you'd have to run a ground line back from the array to the other ground rod. You can't have two independent ground rods in your system. On top of that it is no longer recommended to have separate ground rod by your array. Just run another cable from the array for ground that connects with the ground for the rest of your system. So from your array you will have PV positive cable, PV negative cable, and a grounding cable.

 

[Bluedog225]

Others will know more. Listen to them instead of me.

I believe advice is going to be two grounding rods, greater than 6’ apart, connected by an appropriately sized conductor. That’s the only official earth ground. And everything is run back to that. Including a grounding conductor from your array.

It’s a little fuzzy to me because your array may be grounded as practical matter. That is, connected to the earth. As far as I can tell, it is what it is.

 

[sumya]

No matter what you'd have to run a ground line back from the array to the other ground rod. You can't have two independent ground rods in your system. On top of that it is no longer recommended to have separate ground rod by your array. Just run another cable from the array for ground that connects with the ground for the rest of your system. So from your array you will have PV positive cable, PV negative cable, and a grounding cable.

Okay makes sense. For the grounding cable, i tried putting a #6 bare copper wire through conduit and it was pain the neck. Does it have to be #6 bare copper OR can I connect a #10 stranded wire for this system size which is easier to push through conduit?

 

[marionw]

Of particular interest to PV installers is Section 250-122(b) of the NEC. It states that if the current-carrying conductors have been oversized to minimize voltage drop, then the equipment grounding conductors must also be oversized in the same proportion. But the grounding conductors never have to be larger than the current-carrying conductors. Oversized conductors (above minimum ampacity requirements) are frequently used on long circuits between the PV array and the charge controller to reduce voltage drops in these lines. Table 8 in Chapter 9 of the NEC shows the cross sectional area of different sized conductors, and the calculation is straightforward.

What size (awg gauge) cable are you using for positive and negative from the PV Array (the current carrying conductors)

 

[wdwtx2.0]

Okay makes sense. For the grounding cable, i tried putting a #6 bare copper wire through conduit and it was pain the neck. Does it have to be #6 bare copper OR can I connect a #10 stranded wire for this system size which is easier to push through conduit?

If it it is protected by an enclosure, or conduit, 10AWG stranded should suffice.
As always, the final answer will be provided by your AHJ. They always get the last say.
You only need to have one earth ground point for the system, usually at the main breaker panel.
All grounding conductors connect to it, including grounding conductor for the PV panel frames.
My PV panel arrays are steel pipe, so they are grounded by default, but if they were wood, I would not have driven a ground rod for them.

 

[sumya]

Of particular interest to PV installers is Section 250-122(b) of the NEC. It states that if the current-carrying conductors have been oversized to minimize voltage drop, then the equipment grounding conductors must also be oversized in the same proportion. But the grounding conductors never have to be larger than the current-carrying conductors. Oversized conductors (above minimum ampacity requirements) are frequently used on long circuits between the PV array and the charge controller to reduce voltage drops in these lines. Table 8 in Chapter 9 of the NEC shows the cross sectional area of different sized conductors, and the calculation is straightforward.

What size (awg gauge) cable are you using for positive and negative from the PV Array (the current carrying conductors)

I am using two #10 stranded (red & black) PV wires. So then is it okay to use just one more #10 green stranded wire which connects panels & inverter to one grounding rod?

 

[wdwtx2.0]

I am using two #10 stranded (red & black) PV wires. So then is it okay to use just one more #10 green stranded wire which connects panels & inverter to one grounding rod?

The grounding conductor from the PV panels would tie into the ground bus in your breaker panel.
The grounding conductor for your inverter will need to be sized according to the inverter's output amperage.
The manual for your inverter should state what size to use.
It will also tie into the ground bus in your breaker panel.
There will be a #6 solid copper grounding conductor going unbroken from your breaker panel's ground bus to your ground rod(s).

 

[sumpower]

placed the two ground rods 6 feet apart and as @wdwtx2.0 states, #6 bare copper connected to the panel ground bar on one end and to the 2 ground rods. having no splice in the #6 copper going to the ground rods.
Then run a ground wire with the current carrying conductors from your PV array and ground that at the inverter.
Run a ground wire from your battery to the inverter.
Run a ground wire from the inverter to the ground bar in the electrical panel.

Edit: as a general rule, always run a ground wire with your current carrying conductors. From where the current carrying conductors originate from and to the equipment they terminate at.

 

[robbob2112]

placed the two ground rods 6 feet apart and as @wdwtx2.0 states, #6 bare copper connected to the panel ground bar on one end and to the 2 ground rods. having no splice in the #6 copper going to the ground rods.
Then run a ground wire with the current carrying conductors from your PV array and ground that at the inverter.
Run a ground wire from your battery to the inverter.
Run a ground wire from the inverter to the ground bar in the electrical panel.

Edit: as a general rule, always run a ground wire with your current carrying conductors. From where the current carrying conductors originate from and to the equipment they terminate at.

No ground wire to the battery... No connection to either connection to the battery. Only run a ground wire to the rack the batteries are in or ground screw on the case.

 

[gotbeans]

watch

watch 14:00 - 14:25 that is what your diagram shows, which is dangerous

You want to run a wire from the panels back to your main grounding area to go into that ground rod and only that ground rod

at 14:34 you can see what to do

I am using two #10 stranded (red & black) PV wires. So then is it okay to use just one more #10 green stranded wire which connects panels & inverter to one grounding rod?

yea but you want to bring the grounding straight to the grounding in the breaker, not through the inverter first

 

[Luk88]

It can be made quite simple really. The system should have one equipotential protective ground, but it can (and likely should, unless you have bad soil conditions at pv array site) be composed of many dispersed grounding rods.

Option 1 - You have bad soil conditions(dry clay/rock, or other soil you need to drive 10 rods in to barely get the required ground resistance). Ground the array to the main ground.

Disadvantages? Possibly worse surge/lightning protection than if you had a better ground, but not by much.

Option 2 - Good soil conditions for grounding. Install a grounding rod next to the array.

Then all grounding rods in the system have to be connected directly. So there should be a wire going from the PV grounding rod to where grounding rod no 1 is connected(hopefully thebattery/inverter building electric supply panel). Some recommendations are to have this connection underground, to me a connection that can be inspected is better.

Definitely don't connect both grounds on something like an inverter chassis screw that will corroded in future. If required add a small supply panel that includes a grounding busbar.

The video is nice for people already knowledgable with electric installations, but IMO overcomplicated the matter for beginners.

The thing is, to make an informed decision about it you need to know your soil conditions and if you live in a place where two grounding rods separated by 2m can have extremely different results (one is 2ohms the other 20) the only option is testing.

 

[robbob2112]

@timselectric

'There can be only one'

 

[sumya]

watch

watch 14:00 - 14:25 that is what your diagram shows, which is dangerous

You want to run a wire from the panels back to your main grounding area to go into that ground rod and only that ground rod

at 14:34 you can see what to do
View attachment 217107


yea but you want to bring the grounding straight to the grounding in the breaker, not through the inverter first

With this configuration,
1. I still have to connect inverter ground to sub panel ground, correct?
2. Do I need to do Neutral-GND bond at the sub panel?

 

[robbob2112]

With this configuration,
1. I still have to connect inverter ground to sub panel ground, correct?
2. Do I need to do Neutral-GND bond at the sub panel?

#1 - yes - all panels, boxes shells, PV frames, etc connect to a single grounding connection and that is connected to a single ground rod.

#2 - no - only have the neutral ground bond in your main panel. Make sure your inverter doesn't switch a N/G bond in unless it has a transfer switch and completly disconnects all wires including the neutral. There is generally a settin if this is possible and you want it off

 

[sumya]

#1 - yes - all panels, boxes shells, PV frames, etc connect to a single grounding connection and that is connected to a single ground rod.

#2 - no - only have the neutral ground bond in your main panel. Make sure your inverter doesn't switch a N/G bond in unless it has a transfer switch and completly disconnects all wires including the neutral. There is generally a settin if this is possible and you want it off

# 1 - ok
# 2- Inverter will be connected to a sub-panel with no AC input from main panel. Completely off-grid. In that case, since there is no Neutral-GND bond at inverter or sub-panel, is preference to do it in sub-panel or at inverter?

 

[robbob2112]

# 1 - ok
# 2- Inverter will be connected to a sub-panel with no AC input from main panel. Completely off-grid. In that case, since there is no Neutral-GND bond at inverter or sub-panel, is preference to do it in sub-panel or at inverter?

Personal preference - I would prefer it in the sub panel so I can see the screw verse wondering if the relay in the inverter is on or off.