I have an existing building that is rectangular in shape and we are adding an L-shaped addition to the northwest corner. It is an army corp project and due to ATFP standards, the addition was designed to be self supporting, thus is not structurally bonded to the existing building. The main service for the building isn't particularly close to the new addition and the question came up on how to ground the building steel in the addition. I think the best way to handle this would be to electrically bond the existing building steel to that of the addition with a #1/0 Cu jumper. Review of some prior forum topics would suggest the same. The contractor is raising a question as to where this bond should be made. Is there a certain location where this bond should be made? Any NEC references would be appreciated as I can't seem to find anything to push me in a particular direction.
Grounding building steel of new addition
- Thread starter mac9687
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petersonra
Senior Member
- Location
- Northern illinois
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- Semi-retired engineer
I think this is a seperate structure.
Whatever bond is made would be through the EGC that goes with the feeder to the new structure.
- Location
- Chapel Hill, NC
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- Retired Electrical Contractor
I don't see it as a separate structure. I think it is attached but the building steel is not attached. That's the way I read it.
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
How attached does it have to be to not be a seperate structure?
i can't imagine that the word attached could possibly mean just adjacent.
- Location
- Chapel Hill, NC
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- Retired Electrical Contractor
Are the roofs attached? Does the new building butt up to the existing? If there is no firewall I would call it a single structure.
ceb58
Senior Member
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- Raeford, NC
Are you installing a separate sub panel for the addition? If you are then bond at the new sub panel. If not I would do as you stated install a jumper from the last beam in the old part to the first beam in the new.
I'm with Dennis on this, the way I'm reading it, it is one building.
Are you saying bond from the new sub panel to the new building steel? If so, I don't agree. The new steel is either a grounding electrode if it meets the conditions of 250.52(A)(2), or it is building steel that needs to be bonded in accordance with 250.104(C). In either case, a conductor (a GEC or a bonding jumper as the case may be) needs to run from the new steel to the service or to the existing grounding electrode system. I would suggest a bonding jumper between the old building steel and the new at a location where they come near one another.
Are you saying bond from the new sub panel to the new building steel? If so, I don't agree. The new steel is either a grounding electrode if it meets the conditions of 250.52(A)(2), or it is building steel that needs to be bonded in accordance with 250.104(C). In either case, a conductor (a GEC or a bonding jumper as the case may be) needs to run from the new steel to the service or to the existing grounding electrode system. I would suggest a bonding jumper between the old building steel and the new at a location where they come near one another.
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
Just out of curiousity.
Suppose that your service size required the GEC to the building steel had to be 1/0.
Suppose in lieu of running a bonding conductor between the two steel structures you ran a 1/0 EGC with the feeder to the new part of the building and bonded that to the steel in the new building.
Is that compliant?
Suppose that your service size required the GEC to the building steel had to be 1/0.
Suppose in lieu of running a bonding conductor between the two steel structures you ran a 1/0 EGC with the feeder to the new part of the building and bonded that to the steel in the new building.
Is that compliant?
That depends on whether or not the one conductor can do "double duty" as an EGC and a GEC/Bonding Jumper. I don't think this is spelled out clearly either way in the NEC. I think you could make a case for either opinion. I have heard that there is a change coming in the 2011 NEC that will clarify that the one conductor can't be used for both functions, but I haven't verified it for myself.
kingpb
Senior Member
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- SE USA as far as you can go
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- Engineer, Registered
I would bond the steel together in at least two different locations at the base of the structure using #4/0AWG or maybe even 250KCMIL. The two locations is in case one gets disconnected.
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