Footer rebar verses building steel

[jwelectric]

Just looking for some input for a question that I was asked tonight.

If during the installation of the footer rebar the ?J? bolts for the building steel is anchored to the rebar would a conductor to the steel be the same as a conductor to the rebar or would they both require a conductor?

If the ?J? bolts are tied to the footer rebar I don?t see a reason to bond to both. To hit one would be hitting both.

 

[George Stolz]

Re: Footer rebar verses building steel

I would say that a bonding jumper sized according to 250.66 would be needed to connect the two electrodes together. To the NEC, they're two different electrodes.

This could happen in the concrete, but the only problem is, the connection to the building steel must be accessible - it didn't make the exception from 250.68(A).

 

[don_resqcapt19]

Re: Footer rebar verses building steel

Does anyone else find the fact the NEC calls building steel that does not have direct contact with the earth a grounding electrode?
Don

 

[George Stolz]

Re: Footer rebar verses building steel

Excellent point!

It seems that it should be bonded, but it seems like an odd choice for a "grounding electrode." By definition, it would have to be attached to the ufer to qualify as "effectively grounded."

Proposal?

 

[jwelectric]

Re: Footer rebar verses building steel

This is the exact point that the student pointed out.

That the steel is required to be either, (1)10 feet in the ground, (2)&(3) bonded to one of the other electrodes or (4) Other means of connection to earth.

In 250.52(A)(3) the rebar shall be permitted to be bonded together by the usual steel tie wires. The ?J? bolts are usually tied to the rebar before the concrete is poured and is required to be so in 250.52 (A)(2).

The installation of #4 copper to the rebar and then the installation of a conductor sized by 250.66 to the building steel would make the #4 to the rebar redundant.

I have never thought of this in this manner and can find no reasonable answer to give this student to explain why both conductors are required.


Edited to add:
This is an electrical inspector?s class. This student is already an electrical inspector that is seeking a higher level of certification.

[ October 18, 2005, 10:08 AM: Message edited by: jwelectric ]

 

[don_resqcapt19]

Re: Footer rebar verses building steel

In my opinion the only part of the building steel that should be called a grounding electrode is the part that is in contact with the earth for at least 10'. The steel that is bonded to an electrode would be more correctly called a grounding electrode conductor.
Don

 

[sandsnow]

Re: Footer rebar verses building steel

I have not seen the anchor bolts for the steel directly tied to the steel. I have two new towers coming up so I will keep that in mind.

The usual steel tie wires mentioned in the code, to our city, mean the standard 20 bar diameter overlap required by the building code for splicing reinforcing steel. That is for rebar that is lap spliced. Anchor bolts if connected to the rebar, would not have the same length of metal to metal contact.

The only thing I can surmise is that the anchor bolts are typically 4'long or more down into the column pad and "act" like a UFER, thereby being effectively grounded. 2002 NEC requires effectively grounded.

The bolts being 4' long times at least 4 bolts (usually more) equals 216' feet of bolt encased in concrete satisfying the 2005 NEC.

 

[jwelectric]

Re: Footer rebar verses building steel

Here is a reply to an e-mail I sent asking for more information: I left off his last name and address and removed the name of the company building the building at his request.

Mike,
What I ran into is ____ is building a warehouse type building that will have a 400 amp service. The electrician called for an pad inspection and was present when I got there. He had stubbed a pvc up beside one of the columns and had a 1/0 coper conductor installed and terminated on the rebar with tie wire.
I pointed out that the tie ware was not approved to terminate the conductor to the rebar. He said that he was going to install a lug to the column and run the 1/0 through it before hitting the main disconnect and the anchor bolts was tied to the rebar.
He did change the installation and install a 4 to the rebar with a clamp as I asked. I could see what he was saying but did not know why it was wrong. There will be 16 columns tied to the rebar so why do both?
John

I see what John is talking about. If each anchor ?J? bolt is tied to the rebar in two places and there will be 64 bolts which will be 128 places they are tied. Now if the building is connected to the service with a 1/0 copper conductor the concrete encased rebar will also be bonded by virtue of this 1/0 conductor which would negate the #4 outlined in 250.52 (A)(3).

The only reason that I can give John to do both is because the code says so. I am looking for a reason to do this other that the NEC says so.

 

[don_resqcapt19]

Re: Footer rebar verses building steel

Mike,

The only reason that I can give John to do both is because the code says so. I am looking for a reason to do this other that the NEC says so.

Sometimes that is all that there is...
Don

 

[George Stolz]

Re: Footer rebar verses building steel

How about another setup: the building steel's j-bolts are not connected to the rebar. They are 4' long, so there's 216' of bolt in concrete.

But are these bolts towards the bottom of the concrete where the moisture is higher and the pressure is more intense? I wonder how good of a connection to earth that would be?

 

[sandsnow]

Re: Footer rebar verses building steel

Originally posted by georgestolz:
How about another setup: the building steel's j-bolts are not connected to the rebar. They are 4' long, so there's 216' of bolt in concrete.

But are these bolts towards the bottom of the concrete where the moisture is higher and the pressure is more intense? I wonder how good of a connection to earth that would be?

My post had a typo. It should read 16' not 216'
All thew 2005 requires is 10' of a single structural member in concrete. It doesn't say how deep or where in the concrete.

Under the 2002 you would have an argument because it says >>>where effectively grounded.

How good of a connection??
I would have no idea.
On the other hand, how good does it have to be??