Grounding steel structures - anchor bolts on beams versus footing rebar grounding

[joshtrevino]

When grounding a steel structure, does the NEC dictate if the structure should be grounded via anchor bolts on the steel columns versus grounding of the rebar in the concrete footings?

Is there any advantage of one method versus the other? Best practices?

 

[petersonra]

When grounding a steel structure, does the NEC dictate if the structure should be grounded via anchor bolts on the steel columns versus grounding of the rebar in the concrete footings?

Is there any advantage of one method versus the other? Best practices?

The NEC requires ALL qualifying grounding electrodes to be bonded together. It is possible that the rebar and the metal frame are both qualifying GE. Conversely, there is no guarantee either actually qualifies.

250.50 Grounding Electrode System. All grounding electrodes
as described in 250.52(A)(1) through (A)(7) that are
present at each building or structure served shall be bonded
together to form the grounding electrode system.

Having said that, I am not sure that the structure itself is required to be grounded by the NEC. If the structure's frame is a qualifying GE, the code requires it to be bonded to the electrical system.

250.52 will tell you what qualifies as a grounding electrode.

 

[petersonra]

If the structure's frame is a qualifying GE, the code requires it to be bonded to the electrical system.

I phrased this poorly. What I should have said was this:

If the structure's frame is a qualifying GE, the code requires it to be bonded to the electrical system's grounding electrode system.

 

[iwire]

The NEC also requires a steel frame to be bonded, and in my opinion that must be a direct connection via steel or copper / aluminum etc. not via the concrete in a footing that connects rebar to the anchor bolts.

 

[petersonra]

The NEC also requires a steel frame to be bonded, and in my opinion that must be a direct connection via steel or copper / aluminum etc. not via the concrete in a footing that connects rebar to the anchor bolts.

250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
...
(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.

The way it is worded I think you are right. The frame of the structure can be made to qualify as a GE by reason of it being connected to a CEE.

But I see nothing anywhere that allows you to skip bonding of the various GE together.

 

[electricalist]