Extra/Auxilary grounding rods..... Don't do it.

740GLE said:

Your image is missing the ground at the transformer

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Yes, let's just say assume that is present.

Brett V said:

So in my scenario, the radio tower itself would probably be the separate air terminal...that makes sense.

And I'm not intending to muddy the waters, I realize grounding practices for a large radio tower don't apply to the guy putting a ground mount PV array in his back yard. I wonder how it's done at a large commercial solar farm?

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Size doesn't matter. The code stays the same.

Dagoth Ur Does Solar said:

So maybe this is a stupid question, but doesn't this apply in a similar way to having a grounding rod for a ground-mount solar array?

My amateur understanding has always been you want a single grounding point for your whole electrical system, which under normal residential circumstances tends to be near your feed from utilities/main breaker, everything is tied back here, and you do your NG bond in the main breaker panel.

As in, it seems like a bad idea to have a grounding rod at my shed if I am running electrical service from my home to a sub panel out there. Isn't the idea that my grounding would simply be via the ground wire back to my main panel? Shouldn't the same hold true with grounding a ground-mount array? Wouldn't you want a separate ground wire run along with your PV wire that's tied back into the grounding? I've see people talking about separate grounding rods for this.

Mostly looking for some understanding on this, as to me it seems like the same thing as the shed example.

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You don't need any help. You already understand completely.

Zwy said:

I've read a few of the recent threads and think over time the ground rod requirement may be dropped in NEC.

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It will, definitely.
I just don't know if I will live to see it.
Sometimes the code board moves very slowly.

There are indeed two distinct issues here, although both are talked about under the label of "grounding":

What is correct and proper from an NEC AC and DC electrical code and safety perspective. And what makes sense in protecting your wiring and electronics from lightning and electrical storm induced DC voltages and currents. And while we can say these are (or should be) separate systems, the fact that ground mounted PVs will have a bunch of ground connected steel and aluminum sticking up in the air means they will be potentially subject to lightning, as well them having NEC requirements for grounding on the electrical code side.

The two are in conflict, in that tying your steel mount and PV frames to the common house ground will provide a path for lightning and induced voltages/currents to enter your wiring and equipment. Yet this is the electrical code requirement (as I understand it). From a lightning POV, tying the panel frames and mount to a ground rod at the mount which is not tied to the electrical ground would provide the best lightning protection; but that is not NEC and would require current going thru the ground between the mount ground rod and system ground rod to detect GFI panel faults.

I think this is the basic conflict that keeps coming up on this topic, and I am not sure there is good way to satisfy both concerns. Of course, for inspected systems at least, the NEC requirements will win out. But I don't think that means the lightning concerns go away.

In theory the ground wire between any 2 or more ground rods should keep differential voltage close enough to zero. That's how transmitter sites do it, multiple grounds all strapped together.

Steve777 said:

From a lightning POV, tying the panel frames and mount to a ground rod at the mount which is not tied to the electrical ground would provide the best lightning protection

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That's not lightning protection.
Lightning protection redirects lightning around and away from the equipment. (Not through it)
A Lightning protection system is built (separately) above and around the equipment that you want to protect.

FilterGuy said:

Another nice video from Mike Holt.

Auxilary grounding rods are not required but there is a rule that states there are no requirements on an auxiliary ground e;ectrodes. At one point in the video, he talks about CAT 5 wires and 10 penny nails for the auxiliary grounding electrode.


It has taken several years but we are starting to see both professionals and DIYrs wake up to the fact that auxiliary grounding electrodes are 1) not required and 2) not recommended.

Having said that, I am still a little uncomfortable with the code requirement for a second (not auxiliary) grounding electrode for separate buildings. I would love to see the rationale for this as well as a multi-year study of a bunch of instances where this is not done. The good news is that with just a little planning the 2nd electrode can be set up with the path to the first electrode only going through breaker boxes....but even breaker boxes are starting to get a lot of electronics in them.

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Depending on the distance from the building, grounded equipment can pose a shock hazzard in some areas from the earth contact surfaces without a local electrode.

Supervstech said:

Depending on the distance from the building, grounded equipment can pose a shock hazzard in some areas from the earth contact surfaces without a local electrode.

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From what source?
I have heard this for many years.
I have tested it at 1,500' and got nothing. And this was along side of a river.

timselectric said:

From what source?
I have heard this for many years.
I have tested it at 1,500' and got nothing. And this was along side of a river.

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Oh, a river would be such a high conductivity, as to not pose an issue.
The problems arise when ground is dry, and has very low conductivity.
The locak weather can cause the ground to have a different voltage from grounded surfaces, causing voltage issues.

timselectric said:

That's not lightning protection.
Lightning protection redirects lightning around and away from the equipment. (Not through it)
A Lightning protection system is built (separately) above and around the equipment that you want to protect.

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You’re right, lightning wants to find ground ground, so if there is a direct path to ground from an array or and metal structure straight down, it won’t travel back to your panel .

This is the same for the radio tower, send it straight to ground not back to sensitive equipment.

Supervstech said:

Oh, a river would be such a high conductivity, as to not pose an issue.
The problems arise when ground is dry, and has very low conductivity.
The locak weather can cause the ground to have a different voltage from grounded surfaces, causing voltage issues.

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Then you must be talking about great distance. (Miles? )
In order to have two different local weather conditions.

timselectric said:

That's not lightning protection.
Lightning protection redirects lightning around and away from the equipment. (Not through it)
A Lightning protection system is built (separately) above and around the equipment that you want to protect.

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I should say, best protection if lightning does get to the mount, regardless of other protection...

(on edit) probably more accurate to say it is inverter, CC, etc protection in that if the PV or mount get a direct lightning strike this isn't likely to save them...

Quattrohead said:

In theory the ground wire between any 2 or more ground rods should keep differential voltage close enough to zero. That's how transmitter sites do it, multiple grounds all strapped together.

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In theory, except for two rods a ways apart when a thunderstorm cloud passes overhead. The charge on the bottom of the could will induce a corresponding charge and V potential on the ground underneath. There can be significant voltage differences between ground rods when this happens, with significant currents. Granted, typically not for that long...

740GLE said:

You’re right, lightning wants to find ground ground, so if there is a direct path to ground from an array or and metal structure straight down, it won’t travel back to your panel .

This is the same for the radio tower, send it straight to ground not back to sensitive equipment.

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If the array is metal like the radio tower.
It's already in better direct contact with the earth than any ground rod could accomplish.
But the goal of lighting protection is to not put the array in the path.
Lighting hitting anything is going to damage whatever it hits. There's nothing we can do about it at that point.
Lighting is not going to travel 50' through a #10 grounding conductor. When the earth is less than 10' away. A lighting bolt that has just traveled miles through air, isn't going to blink at the last 10'.
The reason for avoiding the local auxiliary ground rod at the array. Is to avoid any gradient pulse created by a nearby lighting strike. Not a direct hit, that's out of our control.

timselectric said:

Lighting is not going to travel 50' through a #10 grounding conductor. When the earth is less than 10' away. A lighting bolt that has just traveled miles through air, isn't going to blink at the last 10'.

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I've seen hits to a switch yard on surface damage electrical equipment thousands of feet under the ground.

Sometimes especially is very large distributed power systems a strike will use the copper in the power system to dispute through the entire system and not just the closest point in the earth to the where the strike hit

DPC said:

I've seen hits to a switch yard on surface damage electrical equipment thousands of feet under the ground.

Sometimes especially is very large distributed power systems a strike will use the copper in the power system to dispute through the entire system and not just the closest point in the earth to the where the strike hit

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These are magnitudes of differences.
Can't really compare the amount and size of copper in a switch yard to a #10 conductor.
But I digress. We aren't trying to deal with a direct hit. Because we can't. Lighting does what it wants.
I'll say it again.
Grounding a solar array has nothing to do with lighting.

timselectric said:

Then you must be talking about great distance. (Miles? )
In order to have two different local weather conditions.

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Not really.
A structure seperated by a few yards/meters can build up a substantially different charge in the same wind stream.
Think about it...
Its static electricity.
Even IDENTICAL buildings could have different angles to the wind, different paint or siding... all accumulate a different environmental charge.
One bonded to the ground rods, will closely equalize, where the other without rods could have a different charge.

I dont pretend to understand this further, i just accept the explanation i was traind on...

Supervstech said:

Not really.
A structure seperated by a few yards/meters can build up a substantially different charge in the same wind stream.
Think about it...
Its static electricity.
Even IDENTICAL buildings could have different angles to the wind, different paint or siding... all accumulate a different environmental charge.
One bonded to the ground rods, will closely equalize, where the other without rods could have a different charge.

I dont pretend to understand this further, i just accept the explanation i was traind on...

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But if that structure is properly bonded/grounded, there should be no difference in potential.
Especially when we are talking about yards of distance.
I have also tested this at a gravel mine, during various weather conditions, including drought. I don't know the exact length, but it was over 1,000'. Because I was into my second reel, which are 1,000' 1st and 500' 2nd. I just don't remember how much of the second reel was extended.

Supervstech said:

Depending on the distance from the building, grounded equipment can pose a shock hazzard in some areas from the earth contact surfaces without a local electrode.

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Sorry, but if the EGC is ran from building to building, it is a low impedance path compared to not having an EGC and using the ground as a path.

You most likely are thinking of 3 wire feeders from the past and not a 4 wire feeder which contains the EGC. The 3 wire (2 hots and one neutral) will require a ground electrode and N-G bond in the panel for ground fault clearing. A 4 wire feeder has a low impedance path back to the N-G bond at the service panel.