Doubled grounding rods

[Bluedog225]

Would someone explain or point me to a resource on the use of two grounding rods?

I grew up in a world where there was only one grounding rod. But I’ve heard mention of two grounding rods set close together and connected. This is new to me and I’d like to see whether it’s recommended or required or safer or better or what.

And while I’m on the subject, Home Depot has galvanized and copper clad grounding rods. I’m guessing copper is better but wanted to check on that as well.

This is for a completely off grid Victron system. Thanks.

 

[Mike 134]

NEC 2020 sec 250.53A(2) should answer that question.

 

[TimE]

Would someone explain or point me to a resource on the use of two grounding rods?

I grew up in a world where there was only one grounding rod. But I’ve heard mention of two grounding rods set close together and connected. This is new to me and I’d like to see whether it’s recommended or required or safer or better or what.

And while I’m on the subject, Home Depot has galvanized and copper clad grounding rods. I’m guessing copper is better but wanted to check on that as well.

This is for a completely off grid Victron system. Thanks.

Is this for a main earth point for the solar or lightning protection?
When we have designed lightning protection systems we often have multiple rods in a mat. The ground resistance is measured and rods are often up to 4 metres long and numerous to minimise resistance

 

[Bluedog225]

It is for the main (only) electrical system ground.

I may have a separate ground for the panel frames and racking but I have not done that research yet.

I’ll have a look at the NEC and see if I can understand the requirement.

Thanks

 

[Bluedog225]

Well that seems pretty straight forward. ”Shall be supplemented….”

How do I measure the resistance of a grounding rod? I’m guessing a new rod will bear 25 Ohms or less. Do I need to attach to the 8‘ rod at each end to make this measurement? Seems like that would make sense.

Or do they mean the resistance through the earth to another point? That would make more sense to me.

I recall generally that grounding rods connection to earth deteriorates over time. Am I correct in thinking that another rod is best practice?

How do I determine the size of the wire used to bond a second rod to the first?

And what separation between the rods is appropriate.

In looking around, it seems that some recommend just driving two rods and calling it a day instead of testing.

Thanks

 

[Tulex]

Google testing resistance on grounding rods. It requires 2 other rods if I understand, and maybe even specific equipment.
I believe it said minimum of 6 feet spacing.
6 gage copper wire.
Rod and wire really isn't that expensive for the life of the added security.

 

[rhino]

If you can go deeper you will still get far better grounding if you use sectional ground rods where you can screw together two or more rods. You pound one in most of the way and on the top it is threaded where you add a coupler and then screw another rod to top of that coupler.

 

[hwy17]

There's a special expensive tool for it.

So NEC says you can use the special tool to prove your one rod is good, or use 2 spaced appropriately and they assume that's prolly good'n'uff.

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[Bluedog225]

When using two grounding rods per the NEC, do they both have to terminate above the grade? And does the connecting conductor have to be above grade?

Put another way can I pound the second rod below grade and bury the connecting conductor? The first rod will be installed in the traditional way. That is, sticking a couple of inches above grade allowing for easy attachment.

Thanks

 

[LydMekk]

The only reason to use 2 rods with cable between them is to lower the resistance In ohms if it is high with only 1 rod. I would put the bare cable under ground.