Ground Rod Theory

[garbo]

Another flaw I see in this rod spacing or for rods in general is that they're often very close to the foundation so the sphere of influence can be diminished by almost half since there is no earth on one side of the rods.

Wish I had the special meter to read ground rod resistance in my big city concrete jungle. Services enter at back of thousands of row homes that have a common concrete driveway and all concrete from house to concrete driveway. Some houses nearest dirt is over 100' away so even two ground rods would most likely have several hundred ohms to ground. Years ago attempted to illuminate a 100 watt then a 15 watt 120 volt lamp using a ground rod driven into a concrete jungle as the grounded conductor ( neutral ) Had to wait until area was shaded to see the faintest amount of light.

 

[electrofelon]

That's the horizontal joint between the footing and the sill plate.

He's referring to the vertical joint between the footing and the slab.

In my climate, If it's not a one piece structural slab (floating slab, arctic slab) and has a separate foundation and a slab poured inside of it, the slab will be isolated with foam under and on the sides. Pretty much anyplace you have concrete that physically communicates with an interior space, you want it isolated from the ground and moisture.

 

[BarryO]

I understand it's currently a coordination-of-trades hassle while Ufers are used only occasionally, but if they were required for every building, the concrete workers would eventually figure it out. (in a generation or two)

And a coordination-of-inspections hassle. I've seen a pair of ground rods installed in addition to an Ufer solely because the electrical inspector didn't get to look at the rebar before the the concrete was poured. This was back in the 80's; hopefully that doesn't happen anymore.

 

[drcampbell]

... Pretty much anyplace you have concrete that physically communicates with an interior space, you want it isolated from the ground and moisture.

Uff-Dah! I've been thinking about past practices, not best practices for now and the future.
All we need now is electrically-conductive and waterproof thermal insulation.

In residential work, the concrete under the attached garage could be used for an Ufer ground.

 

[ptonsparky]

Uff-Dah! I've been thinking about past practices, not best practices for now and the future.
All we need now is electrically-conductive and waterproof thermal insulation.

In residential work, the concrete under the attached garage could be used for an Ufer ground.

The footings...

 

[Fred B]

Actually it is often a good idea to keep concrete building elements from having direct contact with the soil. Concrete "wicks" water and will result in moisture being released into a conditioned space. Look up "rising damp". If I were to build another foundation I would definitely install a vapor barrier between the footing and the wall. In that case, yes the footing would qualify because it would be in direct contact with the soil. Some may put the vapor barrier under the footing but IMO that is likely to fill up with water and just sit there and be uneffective at it's intended task.

Additionally, many areas and all of NY upstate has adopted some sort of energy code that mandates the use of insulation material under the slab installation thus preventing direct contact with the earth, and negating the use of it for an UFER. Seeing some that are adding water proofing material under and around the footer as well making that unusable too with no direct contact with earth.

 

[AEMCgw]

I had a publication frm AEMC called Understanding ground resistance testing. Its likely out of print, but I suspect the information was based on research done 100 years ago. There may be some background info in the IEEE Green Book

View attachment 2568634 View attachment 2568635 View attachment 2568636 View attachment 2568637

Here's an updated version of this guide: https://www.aemc.com/userfiles/files/resources/workbooks/950-WKBK-GROUND-WEB.pdf
I work for AEMC and lead our technical instruction and assist with creating and editing content to support our products.

 

[ptonsparky]

Here's an updated version of this guide: https://www.aemc.com/userfiles/files/resources/workbooks/950-WKBK-GROUND-WEB.pdf
I work for AEMC and lead our technical instruction and assist with creating and editing content to support our products.

Thank you!

 

[Hv&Lv]

The thing I don't get is that the NEC has gotten to the point where it has become littered with trivial code language yet they let this one stand from 100 years ago. Even when their own informational note in 250.53(A)(3) says that the distance would be better if double the rod length so why not require it?

Well, they had to establish a minimum. That’s really all the NEC is. A minimum standard.

If the calculations say you need a minimum 14 cu in box, there’s absolutely nothing wrong with using a 22 sq in box.

Same with the rods. Place them 15’ apart. No big deal.
Not every locale in the country has enough room to put rods that far apart.

 

[mtnelect]

My indifference to ground rods, is the fact that I live in a city called "Rockcrescenta".

 

[garbo]

We were told at an IAEI continuing education class that the distance when using 8' ground rods should have a minimum of ground rod length or at least 8' apart. Did anybody ever get a minimum of 25 ohms off of a single 8' ground rod? In one of Mike Holts ground rod U tube vidios he had to screw together believe it was a total of 40' of ground rods to get less then 25 ohms. I attempted to illuminate a 100 watt then a 15 watt incandescent lamp off of a 8' ground rod driven into open ground that had recently rained at. The 15 watt lamp ( remember bulbs go into the ground & lamps go into luminares ) had a very faint light produced.

 

[Hv&Lv]

We were told at an IAEI continuing education class that the distance when using 8' ground rods should have a minimum of ground rod length or at least 8' apart. Did anybody ever get a minimum of 25 ohms off of a single 8' ground rod? In one of Mike Holts ground rod U tube vidios he had to screw together believe it was a total of 40' of ground rods to get less then 25 ohms. I attempted to illuminate a 100 watt then a 15 watt incandescent lamp off of a 8' ground rod driven into open ground that had recently rained at. The 15 watt lamp ( remember bulbs go into the ground & lamps go into luminares ) had a very faint light produced.

We screw together 10’ sections of 3/4 rods and drive them 30-40 feet at the substations.
Our spacing is about every 30’ in a grid pattern with 4/0 copper cadwelded to the rods.

 

[letgomywago]

We screw together 10’ sections of 3/4 rods and drive them 30-40 feet at the substations.
Our spacing is about every 30’ in a grid pattern with 4/0 copper cadwelded to the rods.

In places with to high of drainage are there ever gradient issues at the substations or does this design end up evening it all out enough to prevent shock by voltage gradient to the substation guys.

 

[Hv&Lv]

In places with to high of drainage are there ever gradient issues at the substations or does this design end up evening it all out enough to prevent shock by voltage gradient to the substation guys.

The potential exists for voltage gradients in any substation. Hopefully circuits are balanced so there isn’t a lot of neutral currents coming back to the station.

Step potential is the reason substations are graveled with larger stones

 

[letgomywago]

The potential exists for voltage gradients in any substation. Hopefully circuits are balanced so there isn’t a lot of neutral currents coming back to the station.

Step potential is the reason substations are graveled with larger stones

I saw someone try a push a "future city" with grass and tree covered outdoor substations. It was quite the chuckle to see and to see how many people wanted them to look like this without even wondering why do they look the way they do.

 

[drcampbell]

The potential exists for voltage gradients in any substation. Hopefully circuits are balanced so there isn’t a lot of neutral currents coming back to the station.

Step potential is the reason substations are graveled with larger stones

I thought a principal reason was providing leaking transformer oil with an escape route and inhibiting ignition.

 

[Hv&Lv]

I thought a principal reason was providing leaking transformer oil with an escape route and inhibiting ignition.

The last thing you want is an escape route for leaking transformer oil.
We have containment systems in place, whether it’s graveled pits that flow to a oil water Seperator tank, or transformer sitting in the middle of a pit, to making dams at any spots in the yard where the oil could leak out into any adjacent areas

 

[drcampbell]

The last thing you want is an escape route for leaking transformer oil.
We have containment systems in place ...

Um, yeah, that's sort of what I meant. The oil has the ability to freely escape the immediate area of a failed transformer, and sink to the bottom of a gravel pit where it will be hard to ignite, or be extinguished.

Not that it would be free to escape into the environment.

 

[Hv&Lv]

Um, yeah, that's sort of what I meant. The oil has the ability to freely escape the immediate area of a failed transformer, and sink to the bottom of a gravel pit where it will be hard to ignite, or be extinguished.

Not that it would be free to escape into the environment.

 

[ptonsparky]

View attachment 2569571

Is that the set with bullet holes of a few years ago.