Grounding Electrode Options in Non Ideal Soil Conditions

[paullmullen]

I am designing the electrical system for an upcoming residential build. Because of the seasonal high water mark around the property, a good portion of the backfill around the house will be gravel. Furthermore, the walls of this home are being installed as precast off site so concrete encased electrode opportunities are only in a few scattered footing pads.

I'm trying to weigh options for the Grounding Electrode.

OPTION 1: 250.52(A)(5) Though I could put the usual rod electrodes into the gravel close to the basement walls, that probably doesn't really accomplish the connection to earth that such an electrode should provide.

OPTION 2: I could install the electrodes 25 feet away from the home and go into undisturbed soil, but then I have accessible connections sticking up out of the ground in the middle of the yard. A trip hazard for sure.

OPTION 3: I have a couple of footing pads that are in contact with undisturbed soil that seem perfect for a concrete encased electrode per 250.52(A)(3). But this would not be in a location close to the service disconnect. I would be stringing the GEC about 50' around the exterior of the house to get to the service entrance.

Though generally I have placed ground rods relatively close to the service entrance, I do not see any limits in the NEC on the length of the grounding electrode conductor. Did I miss a requirement?

QUESTION 1: Which option - of the ones above - would you recommend?

QUESTION 2: 250.68(A) Exc 1 reads An encased or buried connection to a concrete-encased, driven, or buried electrode shall not be required to be accessible. I had one inspector require accessibility of the connection to the ReBar regardless of this exception. In your opinions, can the grounding conductor clamp to the ReBar extending from the concrete pad be buried or not?

Thanks,

Paul

 

[retirede]

Per code, if a concrete-encased electrode is available, you are required to use it. Otherwise, 2 rods and call it a day.

Option 2 is unnecessary and creates the problems you mention. There is no requirement to establish the effectiveness of the GES unless you only use 1 rod.

 

[petersonra]

What difference does it make? It's not like the earth connection is especially important. Do the bare minimum and be done with it.

 

[infinity]

Will this new building have 1/2" or larger rebar in the footing? If so just use the CEE and call it a day. If you go with option #2, 8' rods are required to be installed 8' into the earth so there will nothing sticking up to trip over. I usually pound them down a few inches below the surface. Once they're inspected they get covered over with dirt. This is pre-inspection.

 

[roger]

Option #1 Rods don't provide much even in the best scenario.
Option #2 The rods could be driven to below ground level but this is a waste of material and labor.
Option #3 As Retired points out, if the footer rebar meets the requirement of being an electrode it must be used.

I would go with #1 and not worry about it.

 

[hillbilly1]

Will this new building have 1/2" or larger rebar in the footing? If so just use the CEE and call it a day. If you go with option #2, 8' rods are required to be installed 8' into the earth so there will nothing sticking up to trip over. I usually pound them down a few inches below the surface. Once they're inspected they get covered over with dirt. This is pre-inspection.

View attachment 2572281

And use acorn clamps, two bolt cannot be buried.

 

[infinity]

And use acorn clamps.

Yes, just like the one in the photo.

 

[paullmullen]

Thanks everyone!

 

[Strathead]

First, precast walls would still have a footer poured in my experience. However, if they put a moisture barrier under the footer then it doesn't qualify for grounding. Second, 25 feet away you don't have to have anything sticking up. The GEC can be connected tot he rods underground or even under concrete with listed irreversible connections or Cadweld. Or, you can put a ground well in the locations.

 

[paullmullen]

Will this new building have 1/2" or larger rebar in the footing? If so just use the CEE and call it a day. If you go with option #2, 8' rods are required to be installed 8' into the earth so there will nothing sticking up to trip over. I usually pound them down a few inches below the surface. Once they're inspected they get covered over with dirt. This is pre-inspection.

View attachment 2572281

Yeah... I was surprised with then local AHJ said "that's not accessible". I caved rather than argue to just get through the project.

 

[paullmullen]

Per code, if a concrete-encased electrode is available, you are required to use it. Otherwise, 2 rods and call it a day.

Option 2 is unnecessary and creates the problems you mention. There is no requirement to establish the effectiveness of the GES unless you only use 1 rod.

Agree. It's about the only thing in the code where "proving that it works" is not an expectation, in practice or in theory.

 

[infinity]

I was surprised with then local AHJ said "that's not accessible".

He should read 250.68(A)Ex#1.

250.68(A) Accessibility.
All mechanical elements used to terminate a grounding electrode conductor or bonding jumper to a grounding electrode shall be accessible.
Exception No. 1: An encased or buried connection to a concrete-encased, driven, or buried grounding electrode shall not be required to be accessible.

 

[paullmullen]

First, precast walls would still have a footer poured in my experience. However, if they put a moisture barrier under the footer then it doesn't qualify for grounding. Second, 25 feet away you don't have to have anything sticking up. The GEC can be connected tot he rods underground or even under concrete with listed irreversible connections or Cadweld. Or, you can put a ground well in the locations.

In this case, the footer is compressed gravel. No reason that it matters, but just adding to the experience. This wall system is Superior Walls (https://glswalls.com/). There's a lot about the system that I like but it adds some new complexity.

 

[electrofelon]

What difference does it make? It's not like the earth connection is especially important. Do the bare minimum and be done with it.

Another thing that should be noted, is if the utility system is an MGN, you will automatically be connected to their super duper ground system that has a far lower earth resistance than anything you could install. I am not saying a lower resistance earthing system matters much. but for those who lose sleep over it, just consider that.