Electrode sizing

C_Hill · Jun 24, 2019

For a 200 amp service, resi., 5/8 by 8' is required. Does a 400amp/320 continuous service require a 3/4 by 10' electrode? I feel like this was something that I had heard about. TIA!

Dennis Alwon · Jun 24, 2019

C_Hill said:
For a 200 amp service, resi., 5/8 by 8' is required. Does a 400amp/320 continuous service require a 3/4 by 10' electrode? I feel like this was something that I had heard about. TIA!

No, the service can be 6000 amps and the ground rod only needs to be 5/8" x 8' or 1/2" by 8' if listed. BTW, welcome to the forum

C_Hill · Jun 24, 2019

Thanking you, Sir.

infinity · Jun 24, 2019

How many rods are you installing?

ManofSteele · Jun 26, 2019

Code Reference

Code Reference

But Where in the NEC does it reference the size and depth of the Ground Rod?

Dennis Alwon · Jun 26, 2019

ManofSteele said:
But Where in the NEC does it reference the size and depth of the Ground Rod?

Here for one

250.52(A)(5) Rod and Pipe Electrodes. Rod and pipe electrodes shall
not be less than 2.44 m (8 ft) in length and shall consist of the
following materials.
(a) Grounding electrodes of pipe or conduit shall not be
smaller than metric designator 21 (trade size 3∕4) and, where of
steel, shall have the outer surface galvanized or otherwise
metal-coated for corrosion protection.
(b) Rod-type grounding electrodes of stainless steel and
copper or zinc coated steel shall be at least 15.87 mm (5∕8 in.) in
diameter, unless listed.

Also

250.53(G) Rod and Pipe Electrodes. The electrode shall be installed
such that at least 2.44 m (8 ft) of length is in contact with the
soil. It shall be driven to a depth of not less than 2.44 m (8 ft)
except that, where rock bottom is encountered, the electrode
shall be driven at an oblique angle not to exceed 45 degrees
from the vertical or, where rock bottom is encountered at an
angle up to 45 degrees, the electrode shall be permitted to be
buried in a trench that is at least 750 mm (30 in.) deep. The
upper end of the electrode shall be flush with or below ground
level unless the aboveground end and the grounding electrode
conductor attachment are protected against physical damage as
specified in 250.10.

jaggedben · Jun 26, 2019

C_Hill said:
For a 200 amp service, resi., 5/8 by 8' is required. ...

Not if the rod is listed.

infinity · Jun 26, 2019

jaggedben said:
Not if the rod is listed.

If you want to go one step further you could say that rods are never required.

ManofSteele · Jul 10, 2019

Got it, Thanks

hhsting · Jul 11, 2019

In what situations one might install 3/4 by 10' ground rod instead of 5/8 by 8' ground rod?

electrofelon · Jul 11, 2019

hhsting said:
In what situations one might install 3/4 by 10' ground rod instead of 5/8 by 8' ground rod?

To meet some silly job spec.

LarryFine · Jul 11, 2019

hhsting said:
In what situations one might install 3/4 by 10' ground rod instead of 5/8 by 8' ground rod?

When I was a helper, our boss (mom'n'pop shop) always had us drive 3/4" RGS as electrodes . . . with a sledge hammer.

ptonsparky · Jul 12, 2019

hhsting said:
In what situations one might install 3/4 by 10' ground rod instead of 5/8 by 8' ground rod?

The customer has the money and asked for it.
Its the only rod you have on the truck.
Job specs.
You’ve had it in the shop for years and are tired of looking at it because you are reminded of that one and only time you goofed up?

Another C10 · Feb 22, 2020

Dennis Alwon said:
No, the service can be 6000 amps and the ground rod only needs to be 5/8" x 8' or 1/2" by 8' if listed. BTW, welcome to the forum

I'm glad I found this answer, I've been searching all over the internet and my ( 2014 NEC) , I know get the latest version .. , and all I found was 250-52 (5) (b) stating the 5/8" rod is approved .. what's with the "unless listed clause" anyway I'd sure like to get a real instance of when that 3/4" inch rod would be required other than a engineers spec.

electrofelon said:
To meet some silly job spec.

I'm sure your right but it's got to have a place somewhere ... one would think. .. I'll followup if I ever decide to spend more time on the mystery ground rod.

Thank you. Sincerely, Mark

infinity · Feb 22, 2020

Another C10 said:
I'm glad I found this answer, I've been searching all over the internet and my ( 2014 NEC) , I know get the latest version .. , and all I found was 250-52 (5) (b) stating the 5/8" rod is approved .. what's with the "unless listed clause" anyway I'd sure like to get a real instance of when that 3/4" inch rod would be required other than a engineers spec.

I'm sure your right but it's got to have a place somewhere ... one would think. .. I'll followup if I ever decide to spend more time on the mystery ground rod.

Thank you. Sincerely, Mark

The rod can be non-listed and have a 5/8" diameter, if it's a listed rod it can have a reduced diameter of 1/2". 3/4" X 10' rods are typically specified when people get all warm and fuzzy about what size the rod is that's pounded into the earth. The NEC is a minimum, IMO I say spec a larger rod if it makes you sleep better at night.

Another C10 · Feb 23, 2020

ptonsparky said:
The customer has the money and asked for it.
Its the only rod you have on the truck.
Job specs.
You’ve had it in the shop for years and are tired of looking at it because you are reminded of that one and only time you goofed up?

Ok But ... were would that 3/4" rod be commonly found, maybe its designed for more surface area in a less conductive soil composition ..?

ptonsparky · Feb 23, 2020

Another C10 said:
Ok But ... were would that 3/4" rod be commonly found, maybe its designed for more surface area in a less conductive soil composition ..?

By code, you would still need at least two, unless that extra surface area got you the 25 ohm. Threaded, they would be used for deep earth.

Guessing. I’ve never seen a 3/4 rod, let alone used one.

I agree with the ‘sleeping well’.

Dennis Alwon · Feb 23, 2020

You can use a 3/4" galvanized pipe

250.52(A)(5) Rod and Pipe Electrodes. Rod and pipe electrodes shall
not be less than 2.44 m (8 ft) in length and shall consist of the
following materials.
(a) Grounding electrodes of pipe or conduit shall not be
smaller than metric designator 21 (trade size 3∕4) and, where of
steel, shall have the outer surface galvanized or otherwise
metal-coated for corrosion protection.
(b) Rod-type grounding electrodes of stainless steel and
copper or zinc coated steel shall be at least 15.87 mm (5∕8 in.) in
diameter, unless listed.

mopowr steve · Feb 23, 2020

Although the only time I’ve driven 3/4”x10 ‘ rods was quite some time ago when the job specs or if we were doing a 400 amp service would do the 3 rods in a triangle. Silly wasn’t it, just how eluding the grounding requirements really were when learning from one person to another.

But as far as a real world use now, one might find it beneficial if you are driving through a hole in concrete where you may get 8’ of rod in contact with soil but a portion may be above ground to attach to.

infinity · Feb 23, 2020

mopowr steve said:
Although the only time I’ve driven 3/4”x10 ‘ rods was quite some time ago when the job specs or if we were doing a 400 amp service would do the 3 rods in a triangle. Silly wasn’t it, just how eluding the grounding requirements really were when learning from one person to another.

We have installed similar triad setups at the corners of the building with 3/4" X 10' rods.

Electrode sizing

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