Grounding rod-Structural Engineer letter 6

[KB2016]

Now a days, most of the city asking a letter after re-bar inspection is done by Engineer. It's not that difficult to issue a letter based on what we observed.
But it makes difficult when city wants Structural engineer add a line " Concrete earth electrode is provided as per NEC 20xx" in the letter. As a structural engineer I have no knowledge about NEC (national Electrical code)so I can't certify that. General contractor is not getting a green tag without engineer letter. They also don't want to hire Electrical engineer for another inspection.
City prospector inspected and gave "okay" but wants letter !!!!!!!What's the best way to tackle this issue. Any suggestion would be appreciated. Thank you

Note: For residential, city doesn't requires a electrical engineer to design electrical. 99% cases Electrical is done(layout) by Architect who provides information based on common practice. GC hires a certified electrician to do the job.
I don't understand why a letter by a PE needed when there is no Electrical engineer is involved!!!!!!!!!

 

[BAretired]

That seems a bit unreasonable on the part of the city. The grounding electrode is not part of the structural engineer's responsibility.

BA

 

[Ron]

KB2016....what the inspector is requiring is illegal for you. You are not allowed by your state law (Texas) to cross disciplines without appropriate qualifications. Don't do it....even for residential.

Tell the inspector that what he is requiring is contrary to state law and not allowed. If he must have an electrical certification, then he needs to get it from an electrical contractor (for residential) or an electrical engineer (all else).

 

[Lnewqban]

It seems to me that the inspector is requesting a statement referring to the concrete part of the grounding, rather than the electrical part.

Copied from:

https://www.thebuildingcodeforum.com/forum/threads/residential-grounding.14560/

"It should be noted that the "piece of rebar" should be tied to at least 20 feet of rebar or #4 copper that is encased in concrete, and the concrete is supposed to be in direct contact with the earth. And this means that if there is a vapor barrier between the concrete and the gravel, that is no good."

Additional links:

http://electricalcodeconnection.com/250-52-a3-concrete-encased-electrode/

https://www.google.com/url?sa=t&rct...jCv-O-0tnSAhXI4CYKHf1PBvYQFggaMAA&url=http://

http://www.burndy.com/docs/default-...iYGIOxs3E15EaD5Pg&sig2=xqMi8Of8XtLZ1FsyNyba-Q

"Engineering is achieving function while avoiding failure." - Henry Petroski

 

[BAretired]

It seems to me that the inspector is requesting a statement referring to the concrete part of the grounding, rather than the electrical part.

1) The concrete must make electrical contact with the earth, i.e. cannot be separated by vapor barrier, so it is the responsibility of the electrical inspector.

2) A structural inspection of the re-bar may be done prior to pouring concrete, so the inspector may not see the concrete portion of the grounding, nor should he be expected to be on hand when it is poured.


BA

 

[KB2016]

I don't have any problem what I observe at the field but i can't just mention in my letter that ......"it's done according to NEC 20xx" because I have no expertise on NEC. Thank you all for your valuable inputs.

 

[thaidavid40]

"A grounding/bonding wire and ground rod were observed connected to the new reinforcing mat. Confirmation of compliance with any code-mandated electrical provisions, including NEC 20xx, shall be left to the qualified electrical professional." Maybe???
Dave

Thaidavid

 

[AUCE98]

Thaidavid40, are you referring to a UFER ground? Ufer ground is a slang term used to describe NEC requirement for concrete-encased electrodes. Which in reality is the grounding lead tied to a rebar mat of a certain minimum size.

 

[dik]

Ron:

I wasn't aware of that restriction in some jurisdictions. We've prepared numerous project drawings with cadwelds to structural steel, chain link fences, SOG reinforcing, pad reinforcing, friction piles, etc. for switchyards, transformer yards, etc. Also show pads and plates for NEMA 2 fasteners.

Dik

 

[JoelTXCive]

In my pre-engineer life, I built residential homes in the Houston area. The slab grounding provisions have been misunderstood and argued about for years.

We would usually attach the slab rebar to the home's ground circuit (see attached diagram). The electricians always said it was the dumbest idea in the world and would often instruct the homeowners how to disconnect after closing. What happens if you are barefoot in the garage or in the shower and your house gets hit by lightening? I don't know the correct answer but it doesn't seem like a real good idea to me. If a large amount of charge goes into the slab and the slab is wrapped in plastic, then how does it get out?

Would the permitting office accept a letter from a licensed electrician? Or maybe you could add a plan comment along the lines of "electrical contractor to provide slab grounding connection pursuant to electrical code section xxxx and any other applicable requirements"

 

[VEBill]

Can the main contractor (the one building the house) use an alternative method of providing the required grounding?

Ground rods, metal plates.

By such means, the rebar is just rebar. Nothing to do with grounding.

 

[jayrod12]

Around here, we ground to the water supply on the city side of the meter.

 

[OperaHouse]

My incoming water pipe is plastic. Encasing a ground rod in concrete makes a very good ground. A very good ground isn't really that good in a high fault current situation. Personally, I prefer to have the concrete I'm walking on be at the same electrical potential of a machine I might touch. Isn't that the idea, to put everything local at the same ground potential. Just recently I was asked about ground problems in a building. A piece of metal laying from the metal building to a cast iron sewer vent was arcing (it was a weld shop where everything was tied to everything). They had hired a contractor some years earlier to fix the ground situation. All I could see was they hammered in two new ground rods. I also noticed that all the concrete ground bars were disconnected. Luckily I didn't have to get involved because my friend quit shortly after that. Legally, I got nothing to add.

 

[dik]

VE1BLL: We often ground the reinforcing since it carries through the concrete... piles, slabs, etc.

Dik

 

[waross]

Ufer ground is a slang term used to describe NEC requirement for concrete-encased electrodes.

Herbert G. may not agree with you.

History

During World War II, the U.S. Army required a grounding system for bomb storage vaults near Tucson and Flagstaff, Arizona. Conventional grounding systems did not work well in this location since the desert terrain had no water table and very little rainfall. The extremely dry soil conditions would have required hundreds of feet of copper rods to be inserted into the ground in order to create a low enough impedance ground to protect the buildings from lightning strikes.

In 1942, Herbert G. Ufer was a consultant working for the U.S. Army. Ufer was given the task of finding a lower cost and more practical alternative to traditional copper rod grounds for these dry locations. Ufer discovered that concrete had better conductivity than most types of soil. Ufer then developed a grounding scheme based on encasing the grounding conductors in concrete. This method proved to be very effective, and was implemented throughout the Arizona test site.

After the war, Ufer continued to test his grounding method, and his results were published in a paper presented at the IEEE Western Appliance Technical Conference in 1963.[1] The use of concrete enclosed grounding conductors was added to the U.S. National Electrical Code (NEC) in 1968. It was not required to be used if a water pipe or other grounding electrode was present. In 1978, the NEC required rebar to be used as a grounding electrode if present. The NEC refers to this type of ground as a "Concrete Encased Electrode" (CEE) instead of using the name Ufer ground.

Over the years, the term "Ufer Ground" has become synonymous with the use of any type of concrete enclosed grounding conductor, whether it conforms to Ufer's original grounding scheme or not.[2]

I consider the doping of the soil and the resulting rise in conductivity to more important than the change from the original copper to steel.
And
Construction
Concrete is naturally basic (has high pH). Ufer observed this meant that it had a ready supply of ions and so provides a better electrical ground than almost any type of soil. Ufer also found that the soil around the concrete became "doped", and its subsequent rise in pH caused the overall impedance of the soil itself to be reduced.[3] The concrete enclosure also increases the surface area of the connection between the grounding conductor and the surrounding soil, which also helps to reduce the overall impedance of the connection.

Ufer's original grounding scheme used copper encased in concrete. However, the high pH of concrete often causes the copper to chip and flake. For this reason, steel is often used instead of copper.

When homes are built on concrete slabs, it is common practice to bring one end of the rebar up out of the concrete at a convenient location to make an easy connection point for the grounding electrode.[4]

Ufer grounds, when present, are preferred over the use of grounding rods. In some areas (like Des Moines, Iowa) Ufer grounds are required for all residential and commercial buildings.[5] The conductivity of the soil usually determines if Ufer grounds are required in any particular area.

An Ufer ground of specified minimum dimensions is recognized by the U.S. National Electrical Code as a grounding electrode.[6] The grounding conductors must have sufficient cover by the concrete to prevent damage when dissipating high-current lightning strikes.[7]

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Gumpmaster]

What is considered sufficient cover to prevent damage during lightning strikes? That seems pretty open to interpretation.

 

[JStructsteel]

Write the letter say you are not familiar with the NEC code, and structurally have no idea if it works per the NEC. Let them scratch their heads at that if they dont get the point by then.

Would they require a Electrical PE to certify the rebar is structurally adequate for the foundation? Same deal. Maybe put that in your letter.

 

[buzzp]

I wouldn't draft the letter either. However, I think about half of the structural guys would - seems to be common practice in some places.
We just throw in a couple of ground rods so he has something to see. NEC never requires more than two ground rods even though they may not have low enough resistance. Rebar embedded in concrete at the lowest level (no vapor barrier) will probably be the best ground around. However, if it is new construction, anything that can be used as a grounding electrode, that is present, must be utilized. We put ground rods in only to satisfy the local inspectors so he can 'see' something.

 

[hacksaw]

It might be that what is being asked for is a letter from a licensed electrician regarding the grounding connections. Have a conversation with the inspector about what is being asked for.

 

[7anoter4]

In my opinion, since the foundation grounding is a pure structural work
the design has to be the result of collaboration between an electrical engineer and a structural one, but the execution inspection has to be done by a building inspector and a legal record of this inspection has to presented for approval.
A field inspection of this installation by a building inspector does not require any specialized training. See-for instance:

http://www.nj.gov/dca/divisions/codes/publications/pdf_bulletins/b_02-2.pdf