I have an electrician calling on a residence we designed a few months back. He never grounded the building steel, just the CWP, and drove a ground rod. We put a grounding detail on our drawings that indicates the building steel is required to be grounded. The construction is CMU block on slab on grade both of which has steel and in my opinion needs to be grounded. Is there any easy way to retroactively go back and make this correct without chipping up concrete? Maybe we're just reading the code incorrectly?
Building Steel Grounding
- Thread starter Npstewart
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Just because the building has steel doesn't mean it is a ground electrode. Metal stud walls aren't electrodes nor is a random column...
I can't tell exactly how much steel you have, what size it is, and what length it is. The intent for structural steel is metal columns all bolted/welded together to make a building frame and a portion of that extending down into the earth for 10' or more. Exact definition from the 2014 code:
250.52(A)(2) Metal Frame of the Building or Structure. The metal frame of the building or structure that is connected to the earth by one or more of the following methods:
(1) At least one structural metal member that is in direct contact with the earth for 3.0 m (10 ft) or more, with or without concrete encasement.
(2) Hold-down bolts securing the structural steel column that are connected to a concrete-encased electrode that complies with 250.52(A)(3) and is located in the support footing or foundation. The hold-down bolts shall be connected to the concrete-encased electrode by welding, exothermic welding, the usual steel tie wires, or other approved means.
Does this slab have rebar that is 1/2" diameter or larger, at least 20' in length, and no plastic barrier under the concrete, so what you have is a concrete encased electrode and not "building steel"? If so, then by 250.52(A)(3) it would be required to be connected to the ground electrode system
I can't tell exactly how much steel you have, what size it is, and what length it is. The intent for structural steel is metal columns all bolted/welded together to make a building frame and a portion of that extending down into the earth for 10' or more. Exact definition from the 2014 code:
250.52(A)(2) Metal Frame of the Building or Structure. The metal frame of the building or structure that is connected to the earth by one or more of the following methods:
(1) At least one structural metal member that is in direct contact with the earth for 3.0 m (10 ft) or more, with or without concrete encasement.
(2) Hold-down bolts securing the structural steel column that are connected to a concrete-encased electrode that complies with 250.52(A)(3) and is located in the support footing or foundation. The hold-down bolts shall be connected to the concrete-encased electrode by welding, exothermic welding, the usual steel tie wires, or other approved means.
Does this slab have rebar that is 1/2" diameter or larger, at least 20' in length, and no plastic barrier under the concrete, so what you have is a concrete encased electrode and not "building steel"? If so, then by 250.52(A)(3) it would be required to be connected to the ground electrode system
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
That steel is not structural steel, it is reinforcement steel in the concrete. Unless it meets concrete encased electrode requirements it is not required to be bonded to anything.
- Location
- Illinois
- Occupation
- retired electrician
It is my opinion that rebar in a slab, no matter what size or how long it is, is not required to be used as or connected to a grounding electrode system.
I don't see a "slab" as being a foundation or footing.
arcsnsparks98
Senior Member
- Location
- Jackson, TN USA
Not to mention a slab is typically poured over a 6mil poly vapor barrier giving it no contact with the earth. Some footing construction methods I have seen isolate them as well.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
A footing that has such insulation barriers applied to it is not a qualifying CEE in accordance with 250.52(A)(3) and is not required to be used as one. There is even an informational note after that section that suggests this.
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