Ground Rod Theory

[LarryFine]

I'm not sure what you are saying here.

I'm saying:

Metallic components shall be encased by at least 50 mm
(2 in.) of concrete and shall be located horizontally within that
portion of a concrete foundation or footing that is in direct
contact with the earth or within vertical foundations or structural
components or members that are in direct contact with
the earth.

Not a slab.

 

[hornetd]

Agreed. I'm saying that even a slab on grade with no plastic would not qualify under any circumstances.

On what are you basing that assertion? If a slab on grade, which is 4 inches or more in thickness, is being used as the foundation and it does not have some nonconductive material between the slab and the earth on which it will sit then the required reinforcing steel or a bare #4 AWG or larger copper conductor can serve as a Concrete Encased Electrode. In that situation you have the opportunity to have an Ufer grounding mat installed by paying the concrete contractor to double tie the 1/2 inch rebar at every tie point. Their is no better grounding electrode nor equipotential plane than an Ufer grounding mat.

Tom Horne

 

[LarryFine]

I love this forum ... Where else could you go to express your opinion ?

Sometimes we're like a gaggle of rabbis, debating every detail in the Bible.

Only our bible is the NEC.

 

[hornetd]

I'm saying:

Not a slab.

Your playing with words there a slab on grade foundation is indeed a foundation.

Tom Horne

 

[LarryFine]

On what are you basing that assertion?

The bold text above.

Their is no better grounding electrode nor equipotential plane than an Ufer grounding mat.

I have never heard the term.

 

[LarryFine]

Your playing with words there a slab on grade foundation is indeed a foundation.

That was not my intention. We have discussed this here before, and the conclusion is that, even with a one-piece-poured footing-and-slab, only the turned-down, deeper sections of footing qualify.

 

[hornetd]

Regardless what you see or hear about on TV weather coverage.

If it bleeds it leads. So of course they pull out whatever video they have of a transformer with a faulted output bursting from the pressure created when the cooling oil reaches it's boiling point from the current flow greatly exceeding it's design.

Tom Horne

 

[hornetd]

I have never heard the term.

Its one of the terms of art used to differentiate a concrete encased electrode from the grounding grid which Herbert Ufer actually devised to protect bomb storage bunkers in the Flagstaff area of Arizona from lightning strikes to prevent the detonation of the stored munitions by internal side flash withing the structure. Just look up Ufer Ground and you will find that a Concrete Encased Electrode is a pale shadow of an actual Ufer ground.

The depth of the turned down edge footer of a slab on grade foundation is not required to be as deep as a footer that is supporting a structure without the strength added by the monolithic reinforcing grid of a slab on grade. look up the specifications for a slab on grade foundation in your locally adopted building code and compare it with the specifications of a footer supported foundation were the structure is supported by a foundation wall of any height and the slab is floating. The footer of the latter type must be both deeper and wider to support the weight of the building.

Tom Horne

 

[wwhitney]

If the reinforcing steel is not 1/2 inch or larger; which would be a violation of all of the model building codes;

Pretty sure that in non-seismic low wind areas, a plain concrete footing is still allowed by the IRC.

then you can install a 20 foot long bare 4 AWG or larger copper conductor in its place. Viz.

You have the option to do so to create a CEE, but the NEC does not compel you to do so to create a CEE.

Cheers, Wayne

 

[electrofelon]

As I wrote above the purpose of system grounding is: "limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation." You are correct in stating that System Grounding has little role in human safety.

Tom Horne

Helping to clear MV faults or contacts with higher voltage lines is the only one of those that has any merit.

 

[electrofelon]

That material is only there to prevent any concrete from infiltrating the soil thus requiring slightly more concrete to poor the footings. They are only a cost avoidance technique. At least one of the model building codes forbids that practice and the inspector can require that a listed material be used for that purpose. The additional cost of a listed material will usually deter the use of such footer trench linings.

Tom Horne

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.

 

[infinity]

Pretty sure that in non-seismic low wind areas, a plain concrete footing is still allowed by the IRC.

You have the option to do so to create a CEE, but the NEC does not compel you to do so to create a CEE.

Cheers, Wayne

As Wayne stated I'm pretty sure that not every structure with a footing requires 1/2" or larger rebar. If it's not required then as stated the CEE is optional.

 

[ptonsparky]

IDK if it's still a thing but fiberglass rebar was getting pretty popular here.
Only the larger area towns require building inspections of any sort other than the Statewide Electrical inspections. I was getting projects that footings were poured and lumber delivered before I knew anything about them. No inspector was there to look at how footings were done.

Some of the crews were getting better about stubbing up a piece of rebar but I had no idea if it went anywhere but straight down.

 

[infinity]

IDK if it's still a thing but fiberglass rebar was getting pretty popular here.
Only the larger area towns require building inspections of any sort other than the Statewide Electrical inspections. I was getting projects that footings were poured and lumber delivered before I knew anything about them. No inspector was there to look at how footings were done.

Some of the crews were getting better about stubbing up a piece of rebar but I had no idea if it went anywhere but straight down.

Around here the building inspector looks for the CEE when inspecting the trench prior to the pour of the footing. No CEE no concrete goes in.

 

[garbo]

So we all know that if you pound in two ground rods they must be at least 6' apart. When you do some research on the spacing between the rods the prevalent opinion is that further is better, something like twice the length of the rods. So for a standard 8' that is 16' apart at the minimum. So why does the NEC only require 6'? And is there a distance that is too far apart?

At an IAEI continuing education class we were told ground rods should be spaced at least the distance they are long. So if you drive two 8' ground rods into the ground d they should be spaced a minimum of 8' apart. Not always easy in large city with concrete al! around. Twice I had nogoodnicks steal the copper wire from ground rods that were 8' apart in a 100% concrete back of house served by a common driveway. Waiting to see if the PVC conduit that I ran rep!acement copper wire last.Told homeowner that he might have to cut a trench in concrete and bury ground wire then cement over it.

 

[kwired]

I'm not sure what you are saying here. The code requires that a piece of bare #4 AWG or larger copper wire 20 feet or more in length or a piece of 1/2 inch rebar 20 or more feet in length encased in not less than 2 inches of concrete on all sides shall be used as the Concrete Encased Electrode. If the reinforcing steel is not 1/2 inch or larger; which would be a violation of all of the model building codes; then you can install a 20 foot long bare 4 AWG or larger copper conductor in its place. Viz.

"250.50 Grounding Electrode System. All grounding electrodes
as described in 250.52(A)(1) through (A)(7) that are
present at each building or structure served shall be bonded
together to form the grounding electrode system. Where none
of these grounding electrodes exist, one or more of the
grounding electrodes specified in 250.52(A)(4) through
(A)(8) shall be installed and used.
Exception: Concrete-encased electrodes of existing buildings or structures
shall not be required to be part of the grounding electrode system where
the steel reinforcing bars or rods are not accessible for use without
disturbing the concrete.

250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(3) Concrete-Encased Electrode. A concrete-encased electrode
shall consist of at least 6.0 m (20 ft) of either (1) or (2):
(1) One or more bare or zinc galvanized or other electrically
conductive coated steel reinforcing bars or rods of not
less than 13 mm (1∕2 in.) in diameter, installed in one
continuous 6.0 m (20 ft) length, or if in multiple pieces
connected together by the usual steel tie wires, exothermic
welding, welding, or other effective means to create a
6.0 m (20 ft) or greater length; or
(2) Bare copper conductor not smaller than 4 AWG
Metallic components shall be encased by at least 50 mm
(2 in.) of concrete and shall be located horizontally within that
portion of a concrete foundation or footing that is in direct
contact with the earth or within vertical foundations or structural
components or members that are in direct contact with
the earth. If multiple concrete-encased electrodes are present
at a building or structure, it shall be permissible to bond only
one into the grounding electrode system."

Tom Horne

As worded if there is qualifying rebar in that footer you must utilize it as a CEE - no requirement to make a non qualifying footer into a grounding electrode though. Is you option to add the #4 copper to turn it into one if you wish though.

 

[kwired]

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.

Doesn't the "sill seal" typically installed under the wall do that?

 

[electrofelon]

Doesn't the "sill seal" typically installed under the wall do that?

It wouldn't matter much if the foundation doesn't extend into a building space. A situation like a basement with lots of concrete surface area it would be more important.

 

[kwired]

IDK if it's still a thing but fiberglass rebar was getting pretty popular here.
Only the larger area towns require building inspections of any sort other than the Statewide Electrical inspections. I was getting projects that footings were poured and lumber delivered before I knew anything about them. No inspector was there to look at how footings were done.

Some of the crews were getting better about stubbing up a piece of rebar but I had no idea if it went anywhere but straight down.

Around here the building inspector looks for the CEE when inspecting the trench prior to the pour of the footing. No CEE no concrete goes in.

That is what is happening in larger area towns that do have building inspections. The rest of the state - electrical is all that gets inspected as there is statewide AHJ for that but building inspection is local jurisdiction thing and for the most part isn't happening in most towns under 2500 population or "out in the county" - some the higher population counties being the exception.

In recent times in these areas a building permit is only for the purpose of examining whether any conditional use permit may be applicable for environmental concerns. 30-40 years ago that wasn't even an issue with wanting to build something around here. Larger livestock facilities is what kind of got that started, now it's wind farms, ethanol plants, oil pipelines, CO2 pipelines and even electric transmission lines that get the attention when someone wants to build any of those, and of course nobody wants any of them in their vicinity yet they want to enjoy any benefits those things may bring them even if fairly indirectly.

 

[LarryFine]

Doesn't the "sill seal" typically installed under the wall do that?

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.