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Bonding Structural steel

Chad Fabry

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Here's the scenario: normal house, footing has re-bar, re-bar is used at the primary grounding electrode (or re-barb as the builder says) , two supplemental 8 ft rods driven at exterior, gas line has some csst and it's bonded as well.

If you were the AHJ, would you consider this statement as a requirement to bond the steel I beams supporting the floor structure?

§250.4(4) Bonding of Electrically Conductive Materials and Other Equipment. Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

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I have seen all manner of energized and likely to become energized materials installed in direct contact with steel beams. That said, I can't recall ever having seen a beam that was bonded.

I think any builder(?) dumb enough to use the word 'rebarb' should be forced to jump through enough hoops to not want to build in your jurisdiction. Stick it to 'em.

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Chad, if this is just supporting the floor frame, and the rest of the building frame is wood, it seems unlikely to be energized. Bonding is never going to hurt, but in this scenario I don't see it being required. I agree with Bill.

The converse of this question comes up fairly often, i.e., when is the building steel a grounding electrode? The answer these days seems to be in the affirmative when it is bonded to the Ufer.

BTW, why did they install the ground rods? If he really did have his "re-barb" as the grounding electrode, and he has a plastic water service, the rods weren't really required. Of course, a lot of local guys want to see them regardless, and I wouldn't quibble over it. As long as they are all bonded together, the more electrodes the merrier.


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Of course, a lot of local guys want to see them regardless, and I wouldn't quibble over it.

Hi Douglas, thanks for weighing in. Our utilities require the first rod unless the Ufer is tested @ 25 Ohms or less. I have no idea why every new house gets the second rod- probably a practice embedded in tradition as much as soil. It's OK with me because I know when I quit there won't be anyone to insist that the foundation steel be made 'available' as the grounding electrode.

I think the second rod is installed because nobody tests the first rod and they think the second rod is required to meet the intent of 250.56

250.56 Resistance of Rod, Pipe, and Plate Electrodes.

A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(4) through (A)(8). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.

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