A Contractor has used the buildings rebar system as a grounding electrode, to connect the transformers throughout the building to ground. NEC states that an acceptable grounding electrode is one that is encased in concrete at the footing all per Article 250.52(A)(3). I believe that this only applies to the 20' of continuous rebar in the footing and this does not extend the electrode all the way up the building to say the 20th floor via the rebar system. The contractor is trying to claim that the rebar is all tied together in the entire building and that this is a steel framing member and thus per NEC Article 250.52(A)(2) it is an electrode. Because this is a concrete structure, I designed the building to include a common grounding electrode conductor of 3/0 up the entire building per Article 250.30(A)(4) with taps to each separately derived system (xfrmr). I believe this section of the code was added to address this specific issue of using the rebar as an electrode as if it were building steel framing member. Article 250.30(A)(7) offers other options for a grounding electrode, which includes all those stated in 250.52(A) if one of the two in 250.30(A)(7) are not available. In no case does the NEC allow the buildings rebar to be used as an electrode, only that portion which complies with article 250.52(A)(3). I know this is confusing but that is my problem also. Is this installation in violation of NEC? And if so which specific Article? Or am I already on the right page by saying a common grounding electrode conductor must be installed (min. 3/0) and connected back to the main service electrode system near as possible to the service or electrode system, and each separately derived system must have a tap to connect to this electrode conductor per Article 240.30(A)(4), and the rebar can not be used?
Building rebar as grounding electrode
- Thread starter barone
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I'll give it a shot but no promises here on beng correct.
Here is a quote from the 2008 NEC The bolded areas are the changes in the 2008.
The vertically seems to allow connection on the vertical rebar but the "within that portion" has me a bit baffled. It would seem that the connection would have to be down low not 20 stories up but that is just a guess.
If you have 3/0 in the specs then I cannot see how the EC can connect 20 floors up on the rebar simply because the rebar, I believe, would only be as good as a #4 copper based on this article. If you require 3/0 then I would assume he must follow the specs whether it is legal or not.
Here is a quote from the 2008 NEC The bolded areas are the changes in the 2008.
The vertically seems to allow connection on the vertical rebar but the "within that portion" has me a bit baffled. It would seem that the connection would have to be down low not 20 stories up but that is just a guess.
If you have 3/0 in the specs then I cannot see how the EC can connect 20 floors up on the rebar simply because the rebar, I believe, would only be as good as a #4 copper based on this article. If you require 3/0 then I would assume he must follow the specs whether it is legal or not.
- Location
- Massachusetts
IMO the only possible way that could fly is if the electrical inspector was given the opportunity to inspect all the re-bar before the pour.
Beyond that I think it meets the letter of the code even if not the intent.
Beyond that I think it meets the letter of the code even if not the intent.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I don't believe the rebar is a steel framing member as used in the code.
I do think the contractor has a good point that as long as the rebar is all tied together that he is probably code compliant.
If the plans or specs call for something else, that is not really a code issue, but a contract issue.
I do think the contractor has a good point that as long as the rebar is all tied together that he is probably code compliant.
If the plans or specs call for something else, that is not really a code issue, but a contract issue.
cripple
Senior Member
- Location
- Santa Fe, New Mexico
To be able to meet the requirements of Section 250.52(A)(3)
? First, the rebar shall consist of at least 20 ft of one or more bare or zinc galvanized or other electrically conductive-coated steel reinforcing bars or rods of not less than 1/2 inch in diameter.
o If the footing or foundation does not permit the installation of 20 feet of rebar, you stop and install one of the other electrode systems permitted by section 250.52.
? Second, if the footing or foundation does permit the 20 feet now the rebar shall be encased in at least 2 inches of connected and shall be located horizontally near the bottom or vertically.
o If that portion of a concrete foundation or footing that is not in direct contact with the earth for at least 20 feet, this section cannot be applied.
As for use of steel framing members, the NEC does not require the steel-framing members to be bonding, so how can it be permissible them to use as grounding electrical.
However the Code does permit the use of structural metal member that met all the requirements of Section 250.51(A)(2).
? First, the rebar shall consist of at least 20 ft of one or more bare or zinc galvanized or other electrically conductive-coated steel reinforcing bars or rods of not less than 1/2 inch in diameter.
o If the footing or foundation does not permit the installation of 20 feet of rebar, you stop and install one of the other electrode systems permitted by section 250.52.
? Second, if the footing or foundation does permit the 20 feet now the rebar shall be encased in at least 2 inches of connected and shall be located horizontally near the bottom or vertically.
o If that portion of a concrete foundation or footing that is not in direct contact with the earth for at least 20 feet, this section cannot be applied.
As for use of steel framing members, the NEC does not require the steel-framing members to be bonding, so how can it be permissible them to use as grounding electrical.
However the Code does permit the use of structural metal member that met all the requirements of Section 250.51(A)(2).
- Status