Light Gauge Metal framing

[jfcroft]

We have a school project where the construction is light gauge metal trusses/roof decking sitting on top of CMU walls. There is a debate between the Electrical Contractor, the Owner, the Electrical Inpector(s) and the Engineer as to whether the light gauge metal trusses may be utilized as the Grounding Electrode Conductor. This project was constructed under the 2002 N.E.C. Presently, the metal truss system is being utilized as the GEC as the contractor interpreted it as building steel. It is the Engineer's (my firm) opinion that so long as the trusses are continuous, this is an acceptable GEC. Where the trusses may not be continuous, a bonding jumper may be used to make them continuous.

Thoughts? Can a light gauge metal truss system be used as the GEC so long as it is continuous and complete?

 

[iwire]

Thoughts? Can a light gauge metal truss system be used as the GEC so long as it is continuous and complete?

In my opinion yes.

The following is from the 2002 NEC

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, where effectively
grounded.

In my opinion if the frame of your building meets the above you may also use it as Grounding Electrode Conductor.

Also from 2002

250.64 Grounding Electrode Conductor Installation.
Grounding electrode conductors shall be installed as specified
in 250.64(A) through (F).

(F) To Electrode(s). A grounding electrode conductor
shall be permitted to be run to any convenient grounding
electrode available in the grounding electrode system or to
one or more grounding electrode(s) individually. The
grounding electrode conductor shall be sized for the largest
grounding electrode conductor required among all the electrodes
connected to it.

 

[Smart $]

...construction is light gauge metal trusses/roof decking sitting on top of CMU walls. ...

Thoughts? Can a light gauge metal truss system be used as the GEC so long as it is continuous and complete?

I agree the truss system is metal frame of the building. However, just by itself, it is not a GEC. In order to qualify as a GEC, it must be connected to earth by direct contact, bonded to one or more grounding electrodes, or other approved means.

PS: Is this concerning an alteration to the current system, and if so, what code cycle is the alteration under?

 

[iwire]

In order to qualify as a GEC, it must be connected to earth by direct contact, bonded to one or more grounding electrodes, or other approved means.

In his case it only has to be 'effectively grounded' and only the AHJ can answer that.

 

[Smart $]

In his case it only has to be 'effectively grounded' and only the AHJ can answer that.

I'm assuming this is regarding new work that is under a newer cycle.

 

[don_resqcapt19]

I don't see metal framing sitting on top of CMUs as a metal building frame.

 

[Smart $]

I don't see metal framing sitting on top of CMUs as a metal building frame.

Seems you have a contradiction of terms there...!!!!

The code doesn't say the entire building or structure must be constructed of metal framing.

 

[iwire]

I don't see metal framing sitting on top of CMUs as a metal building frame.

I don't see how it could be anything but.

It may not be an electrode but it is a building frame.

 

[jfcroft]

A little background. We had another project with the same contractors that had some "shock" occurences. Investigations found that the secondary transformers were not connected to an effective ground electrode. The contractor corrected the installation. The Owner became concerned and investigated another project (the one in question) and is of the interpretation that it is not correctly grounded as well. We did some research and found that the contractor had connected the transformers to the light gauge metal truss system, but there was nothing connecting the light gauge metal truss system to a grounding electrode. We issued an opinion that installing a bond between the metal truss system and the grounding electrode, in this case the domestic water entrance riser, would create an effective grounding electrode. The AHJ has agreed with this interpretation. The Owner disagrees and wants us to find a reason that the metal truss system cannot be used. We cannot find one.

 

[pete m.]

I don't see how it could be anything but.

It may not be an electrode but it is a building frame.

I thought at one time we had this same discussion over a metal I-beam that ran the length of a residential basement carrying the floor joists and using it as a grounding electrode and/or GEC?

IIRC the consensus was that it was not cosidered a building frame.

http://forums.mikeholt.com/showthread.php?t=57577&page=2

Pete

 

[pete m.]

Here is another link.

http://forums.mikeholt.com/showthread.php?t=58072

I know we are talking about a metal truss system but I see it no differently than I would steel joists and girders resting on CMU walls.

Pete

 

[cadpoint]

I don?t know what side you?re taking in the argument! I would think that three out of the four could be knocked out of the disagreement via the State Inspector. If it?s not a State job than two out of the four could be knocked out of the conversation via the State Electrical Board.

My biggest argument is that the stud guy can?t even put in four screws in four corners, so they don?t even build the product to their own design or manufactured specific application. What about expansion joints, hello there?s your gap!

Just because they got away with it in 2002, they can?t go back to the way they did it then or for 2008 or now 2011. TN is under 2008. What did they us BX?

Let the Big boys have something to do in Nashville, unless you?re in exempt Jurisdiction.
http://tn.gov/commerce/sfm/electInsSec.shtml

 

[pete m.]

I don?t know what side you?re taking in the argument!

Yea I don't have a dog in the fight. As far as what side I'm on.... whichever one is right. :happyyes:

Pete

 

[jfcroft]

I don?t know what side you?re taking in the argument! I would think that three out of the four could be knocked out of the disagreement via the State Inspector. If it?s not a State job than two out of the four could be knocked out of the conversation via the State Electrical Board.

My biggest argument is that the stud guy can?t even put in four screws in four corners, so they don?t even build the product to their own design or manufactured specific application. What about expansion joints, hello there?s your gap!

Just because they got away with it in 2002, they can?t go back to the way they did it then or for 2008 or now 2011. TN is under 2008. What did they us BX?

Let the Big boys have something to do in Nashville, unless you?re in exempt Jurisdiction.
http://tn.gov/commerce/sfm/electInsSec.shtml

We are of the opinion that, with the added bonding between the truss system and the grounding electrode, the truss system becomes a Ground Electrode Conductor. We have placed a call into the State Electrical inspector to obtain an official ruling. He won't issue a ruling until he can see the installation which, of course, is covered up by a rated ceiling assembly. Time to install some rated access doors.

Yes, TN is currently under the 2008 Code. The building was designed, built and inspected under the 2002 Code which is what is being enforced in the corrective actions.

 

[don_resqcapt19]

I don't see how it could be anything but.

It may not be an electrode but it is a building frame.

I see it as part of a building frame, not a building frame.

 

[jfcroft]

I see it as part of a building frame, not a building frame.

The Code is not specific in that regard. It does not say it has to be the whole building frame. Likewise, it doesn't say it cannot be framing for parts of the building.

 

[Smart $]

I see it as part of a building frame, not a building frame.

But where does it say building frame? It says, "The metal frame of the building or structure..." I interpret that as any structural framework that is metal, whether all or part of the building frame.

 

[don_resqcapt19]

But where does it say building frame? It says, "The metal frame of the building or structure..." I interpret that as any structural framework that is metal, whether all or part of the building frame.

And I choose to read it as requiring a complete metal building frame, not just part of one. Lacking a FI from the NFPA, I will continue to read the section as requiring a complete building frame.

 

[Cow]

I didn't read the whole thread, but I had this conversation with our state inspector a while back. He only considered it building steel if there were posts down to the ground. Metal trusses alone didn't cut it. Makes sense to me.

 

[pete m.]

Time for my education....

I have understood the reason the CMP made the change for only being able to use the first 5' of water line for a GEC connection was because it was common to make a repair in the line using plastic.

So if we were to look at a metal component of a building such as bar joists, a steel beam holding up floor joists in the basement of a house, a metal roof truss system, etc... How easy would it be to replace any one or part of one of those components with something other than steel without compromising the structure?

How often does this actually happen? Is there less likelihood of losing a GEC path because of steel being replaced with something non-conductive?

Let the education begin :happyyes:

Pete