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We live on a pile of cobble and boulders (glacial outwash) which makes driving ground rods close to impossible. Is it permissible to bury a ground rod or a plate, and if so, what are the requirements?

If burial is legal, can a rod be buried in the trench carrying the feeder wire? Could two rods be placed 8' apart in the trench? Or driven as far down as possible and then bent at an angle so they just come above ground?

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    How have you tried to drive them? If you haven't already, rent an SDS max hammer driver with a ground rod driver and see how impossible it is then. Sep 2, 2022 at 6:10
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    An Ufer ground may be an option
    – Jasen
    Sep 2, 2022 at 10:36
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    Would ask the local power company/electrical inspectors. Your land sounds like having enough connection to make ground rods/plates useful is iffy. Not much sense listening to us, if inspector comes after and tells you that was a waste of time and money. They might have a simple cheap way for your location.
    – crip659
    Sep 2, 2022 at 11:19
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    Where in the world are you located? The local code will determine what you're (not) allowed to do.
    – FreeMan
    Sep 2, 2022 at 12:05
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    @Jasen A Ufer ground is installed in the foundation of a house when it is poured, I doubt that's an option here. Sep 2, 2022 at 13:50

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I live on a similar patch of glacier barf, having pulled out multiple rocks of golden retriever up to small cow size in various work, and managed to drive 5 grounding rods with a plain old post driver and sledgehammer. Specialized drivers can be called in if those prove inadequate.

4 of them are in the bottom of the incoming power trench, but they are driven full depth from the bottom (so they are 11 feet down at the tip, starting from 3 feet down, in undisturbed soil.) My electrician of the time was a lazy sort who said I could have just laid them flat in the bottom of the trench and met code, (and, of course, that I only needed 2) but it really wasn't difficult to do better than that. The clamps have to be burial rated, of course, but most are.

If you haven't already poured the foundation, a concrete encased electrode (Ufer ground - using the rebar in the concrete) would be a better option.

A plate electrode "exposing at least 2 square feet of surface area" can be buried at least 30 inches deep.

The type of soil you have is a relatively poor one for making effective contact with grounding electrodes. Consider using more than the minimum, and especially the concrete-encased variant (if it's not too late for that) as being the best type to really work well despite your soil type.

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  • Thanks for ideas. Ufer is not an option as this is a pole shed with no foundation. I'm more concerned with a good ground that minimum code. How far apart are the rods in the trench -- 8 feet? Sep 2, 2022 at 22:31
  • 10 or 12 feet, I think. "ideal" is twice the length of the rod (so 16 feet) or more, but I think they ended up slightly closer than that. Code minimum is 6 feet apart. I also bolted to the 100 foot steel well casing.
    – Ecnerwal
    Sep 3, 2022 at 0:32
  • Thanks. I wish my well casing was closer; it's probably a far better ground than anything else around here. It's about 30' from the house but 200' from this project. Should have used it when I wired the house. Sep 3, 2022 at 19:48
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NEC gives that to local jurisdictions to decide.

This question is NOT set in stone in the NEC. That is on purpose, because different localities have different soil types, to use the word loosely. And so, they give local AHJs the freedom to adjust ground-rod requirements to local conditions.

A Louisiana bayou locality may know that any ground rod is going to test out at 5-10 ohms, so there will never be a need for that second ground rod.

Or in a municipality like yours, they will know about the rocky soil and have sensible alternatives.

So, the answer is check with your AHJ and ask what they consider to be acceptable.

As a practical thing, the more ground rods the better. The ground rods have an important job other than getting your permit signed off.

...But you could side-step it with one word.

The word is "Ufer". And it needs to be said to your foundation guy/concrete guy.

An "Ufer" ground ties into the steel reinforcing rod in your poured basement, foundation or slab. It is a trivial add-on at the time that is being poured (harder to retrofit later). It is by far the most effective grounding method known, and works anywhere.

Ufer is the last name of the person who invented it.

But a huge number of Ufer grounds are not created when it is easy, simply because people forget to ask for it or there's a snafu with the contractor. If I were king, there'd be a $50 excise tax on any building pour done without an Ufer ground. Just like that, no contractor would ever forget the Ufer, they'd be putting Ufers on sidewalks and retaining walls LOL.

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    "This question is NOT set in stone" -- PUNintentional? :)
    – FreeMan
    Sep 9, 2022 at 12:56
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    @FreeMan a little. Of course it's encouraged to be set in concrete :) Sep 9, 2022 at 17:52
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Digesting all of the comments and answers above, I borrowed a Hitachi H45FRV hammer-driver from a friend. It took at least 30 min of driving, possibly an hour, spread over six hours, to drive each of two 5/8"rods.

I first started a hole with a custom "willow tree planting" bit, similar to a concrete breaker only longer (~3 ft long, 3/4" dia, pointed tip). The main reasons for that were to get a hole which would funnel water deeper, and get the top of the rod low enough it was more easily reachable. The rods are in the trench at one side, about 8" from the conduit.

I then started a hose and filled the hole and a surrounding puddle to keep a reservoir of water available to drain into the hole and down the side of the rod. It took 5-10 min to drive a rod 1.5 - 2 feet, at which point 2-4 min of solid driving got no-where. I alternated 2-4 min of driving from one rod to the other about 3 times. With no success, I left the hose dribbling into one of the puddles and did something else for a while (30 min to 1hr). I then tried again, but another 5-8 minutes of driving in 2-4 min sessions alternating between rods made no further progress. I left the hose dribbling...

After another couple of hours I tried again and was able to go down another 3 feet or so. Hammer more, keep the hole filled with water, wait a few hours, and eventually I got both rods in.

I don't know how the Hitachi compares to a Hilti SMS Max mentioned in this post; but it's what I had available.

I didn't have a proper ground-rod driving bit, and I couldn't find one in the nearest (65 mi away) "metropolis". But the Hitachi head has a 3" or so deep collar that engages the bit. The bits have a flat spot in which a locking pin sits to keep them from sliding out when the driver is pointing down. You pull back a knob to retract the locking pin; turning the knob leaves the pin retracted. The bits are 3/4", so a ground rod fits in the bit-hole fairly well, and with the locking pin retracted, it's a pretty good arrangement.

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    I take it that a concrete-encased (Ufer) ground isn't an option where you live for some reason or another? I'm not sure if you can meet 25ohms even with 2 rods given just how awful your conditions seem to be...(you may wish to have a fall of potential test run on your newly installed rods) Sep 9, 2022 at 2:04
  • @ThreePhase No, this is a 2-sided pole shed, so no concrete anywhere. I've wondered about an ufer here; the soil drains so well and eves stick out 3'. Even with 4' of snow there is never snow at the foundation wall. I am considering running an extra ground from house to the well-casing, which is 65' down to water. Conductivity of the casing isn't great, but seems like the best option. If I did a fall-of-potential test, what options would I have once I got the answer? Tie to REA ground at the xformer? Already done on their side, so no point? Probably not legal or allowed anyway. Sep 9, 2022 at 15:21
  • What are you building the pole shed on (i.e. what are you using for a foundation for it)? And yes, a metal well casing is a fantastic ground electrode -- I'd say it's about the only thing that's anywhere comparable to an Ufer, even Sep 9, 2022 at 23:16
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    @ThreePhase A pole barn/shed is generally built on the ground with no foundation, no concrete pad -- it's supported by poles set in holes in the ground. The poles may or may not have concrete pads of a diameter somewhat larger than the pole, depending on soil type. The poles for this shed are in holes 4 feet deep with no pads. Sep 10, 2022 at 5:05
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Not sure if putting the rods by the feeder wires is allowed, but I think it's a bad idea, as the grounding electrodes are intended to make contact with normal soil and the feeder wire trench will have sand and other materials rather than just dirt. A slit trench 30 inches deep should work fine, and the grounding electrode conductor can be run inside to connect the two buried rods.

250.53 Grounding Electrode System Installation National Electrical Code 2020 of Illinois

(A) Rod, Pipe, and Plate Electrodes

Rod, pipe, and plate electrodes shall meet the requirements of 250.53(A)(1) through (A)(3).

(1) Below Permanent Moisture Level If practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel.

(2) Supplemental Electrode Required A single rod, pipe, or plate electrode shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(8). The supplemental electrode shall be permitted to be bonded to one of the following:

Rod, pipe, or plate electrode
Grounding electrode conductor
Grounded service-entrance conductor
Nonflexible grounded service raceway
Any grounded service enclosure

Exception: If a single rod, pipe, or plate grounding electrode has a resistance to earth of 25 ohms or less, the supplemental electrode shall not be required.

(3) Supplemental Electrode If multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart. Informational Note: The paralleling efficiency of rods is increased by spacing them twice the length of the longest rod. (4) 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.

...

(C) Bonding Jumper The bonding jumper(s) used to connect the grounding electrodes together to form the grounding electrode system shall be installed in accordance with 250.64(A), (B), and (E), shall be sized in accordance with 250.66, and shall be connected in the manner specified in 250.70. Rebar shall not be used as a conductor to interconnect the electrodes of grounding electrode systems.

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  • Unfortunately, "soil" doesn't exist here below about 2". Literally. It's rock and gravel; sand would be a delight if there was any. Sep 2, 2022 at 22:55

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