ECN Forum Forums Code Related Discussion NEC & other Code issues Structural Steel

I hope you guys are aware that there are two Georges on this page and I (George Little) agree with Don. I'm not sure about George #2

Yeah, I almost said 'George not little'

IMO...parts of 250.104(C) are vague and open to interpretation by the AHJ.

For instance,"may become energized"...could mean a number of different things to me. May become energized by wiring that is attached to the steel...or may become energized by a faulty extension cord coming in contact with the steel...or may become energized by a lightning hit to the building. How about stray voltage that may be present in the earth seeking a path throught the concrete to the steel set upon it? We are concerned with this stray voltage around pools,wouldn't this structural building steel in George Little's 1st post be exposed to stray voltage from maybe, deteriorating utility neutral conductors in the area like a pool would? Probably not as much as a pool but there is a possibility that it May Become Energized.

250.104(C) also doesn't state how much steel has to be interconnected to form a building frame.Is it a complete frame structure or a couple of pieces of steel forming a partial structure as in George Little's post? The definition of structure in article 100 is "That which is built or constructed"... so those 2 pieces of steel seem to be a structure to me.

Yes...I think it is open to interpretation by the AHJ...IMO

shortcircuit

I hope you do not become an inspector in MA.

Forget about the pool example, the bonding in a pool area has little to due with keeping the parts from being energized. It has to due with keeping the parts at the same potential. There is a difference.


Here is some info on that from the handbook following 680.26


Exposed structural steel that is interconnected to form a steel building frame to me means a building that has a steel skeleton not a wood building that has an occasional steel member.

To each there own, I would fight it if it was a cost issue.

We work in some old mill buildings that are made of brick and wood, in many places the horizontal timbers have been 'sistered' with steel channels. I would not accept an inspector telling me I have to bond all of these with a separate pieces of steel on the upper floors back to the service with a conductor based on 250.66.

JMO, Bob

Yes bonding of a pool primary fuction is to eliminate voltage gradients that may be present. But it also brings the structure of the pool and all associated equipment to the same potential in case something were to become energized. Bonding of a pool and bonding of a buildings structural steel are alike...there are both keeping parts of a steel structure and electrical equipment at the same potential in case they do become energized.

Isolated sections of steel on the upper floors as you have described in the old mill are different than the structual steel setting on concrete in direct contact with the earth as I assume is the exsample in George Little's post.

If 250.104(C) intended to mean a complete steel skeleton forming the structual steel of a building need only be bonded...then it should say just that. But it can not. Surely someone would hang if somebody were to be hurt coming in contact with George Little's steel structure that was energized and not properly bonded because 250.104(C) only meant to bond complete steel structures forming the skeleton of a building.

My opinions are based on what I've been taught by instructors. This forum is a place to voice opinions of how things are done in the industry and interpretations of the codes applied to them. If I am wrong about something, then please correct me. I am here to learn.I don't see the need for the inspector comment...

JMO, shortcircuit

I disagree, the section in question 250.104 is not all about keeping everything the same potential, that section is there to cause an overcurrent device to operate if the steel becomes energized by a circuit conductor.

The bonding at a pool is there to keep all things that you can come in contact with at the same potential even during a fault condition when that bonding system has a potential above earth.

Isolated sections of structural steel are not a pool, a pool is different, pools have different bonding requirements because they are....well..different.

I mean no disrespect here but I have no idea why you think that "structural steel setting on concrete in direct contact with the earth" in of itself is dangerous.

If thats so should I bond my child's swing set?

What about a metal folding chair sitting on a concrete slab?


Please explain how this isolated piece of steel would be affected by a bad utility neutral.



There is no path until you bond it.

Current does not flow without a complete circuit.

I would take back the inspector comment but statements like this;


Leads me to believe you have a serious misunderstanding of this section.

If we accept your extension cord scenario the next question would have to be why limit bonding to isolated sections of structural steel, why not require all metal objects in a building to be bonded?

File cabinets, suspended ceiling grids etc.

At any rate we have certainly proved George Littles point.

I feel I should say my opinions are my own and not those of ECN.

All are welcome to disagree.

Bob



[This message has been edited by iwire (edited 02-13-2005).]

The bonding of structural steel has become an issue in our area as well. I think the wording could be worked with for clarity.

1. It does not say the frame of an entire building. I have seen (especially in residential) portions of the framing to be ofmetal and portions to be of wood.
I think the 2 keys here are "may become energized" and "Exposed Structural steel", not one or the other, but both items have to be present at the same time.
In the residential buildings I mentioned, most of the time the steel is concealed at final construction, so it becomes a moot question. Otherwise how would one make the connection "accessible"

This is a little off base on a tangent of bonding structural steel, but in one jurisdiction that I worked in, I had to bond the aluminum siding of a house with #6 copper and a lug bolted to the siding. Seems it was a local law that was passed after a town councilman's daughter got shocked by some stray current from an outside light.

I am concerned about(exposed)structural steel setting concrete in contact with the earth because it establishes a Ground-Fault Current Path.

250.2 Definition..."Ground-Fault Current Path"...
An electrically conductive path from the point of a ground fault on a wiring system through normally non-current-carrying conductors,equipment,or the EARTH to the electrical supply source.

FPN:Exsamples of ground-fault paths could consist of any combination of equipment grounding conductors, metalic raceways, metallic cable sheaths, electrical equipment, and any other electrically conductive material such as metal water and gas piping, STEEL FRAMING MEMBERS, stucco mesh, metal ducting, reinforcing steel, shields of communications cables, and the EARTH itself.

Surely George Little's steel framing would have to be evaluated by the AHJ to see if it were to present a hazard.

Concrete floors in contact with the earth do establish a path through the earth to the supply source. We GFCI most 15 and 20 amp receptical outlets in these areas because of this.

Article 100 Definition of "Bonding"...

The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to carry ANY current likely to be imposed.

There is only one definition of bonding...not one for swimming pools and one for everything else.

shortcircuit

A column and a beam is not "exposed structural steel that is interconnected to form a steel building frame" and therefore the code does not require bonding.
CMP 5 made the following panel statement in comment 5-111 in the 95ROC.
The words "single family dwelling" were used only in response to the submitters words in his comment. It is my opinion that isolated supports like these in any occupancy are not required to be bonded as the are not a "steel building frame".
Don

[This message has been edited by resqcapt19 (edited 02-14-2005).]