Metallic joist and decking roof qualify as grounding electrodes?

[marcosgue]

Hello all, there's a new construction for school with block and concrete structure and some columns going up to the roof.
the roof is build with metallic joist and metallic decking at the top. does this type of roof qualify as grounding electrodes for the grounding electrodes system? Can we consider this as metal frame of the building to bond, let say the system bonding jumper for a SDS?
Thanks all in advance

 

[LarryFine]

I believe the correct answers are no and yes, respectively.

 

[marcosgue]

which would be the factors for the right answer?

 

[Dennis Alwon]

Well the roof can in no way be considered an electrode as acceptable electrodes are mention in article 250 and all have contact in the earth. The roof is probably bonded thru the steel columns of the building.

 

[LarryFine]

Okay, if there are steel columns bolted to qualifying foundations, the steel structure can be an electrode.

As a continuous steel structure, the building metal may be used as part of the electrode jumper pathway.

 

[marcosgue]

yes, the roof is bonded thru the steel columns, however there's no grounding electrode (CEE, metal water pipe,) accessible to electrical room to bond the grounding electrode system and the SDS and someone says bond to the roof is acceptable, I believe this's not correct.
this would be an acceptable method in this specific situation?

 

[marcosgue]

the things is no accessible point in the building metal to bond an effective pathway. I think the only way to bond the electrical system is drive a ground rod instead the use of the structural metal of the roof. Am I correct? any suggestions

 

[Dennis Alwon]

Am I correct in saying that you are adding a transformer and you need to get to an electrode. If so, then the steel may very well be part of the electrode system but IMO the roof would not be.

 

[LarryFine]

When you say "metallic roof", are you referring to an entire bolted and/or welded steel girder-and-truss system, like you'd see in Costco, or just a sheet-metal roof on a non-conductive framing system like you'd find in a pole barn?

 

[marcosgue]

Yes Dennis you're correct, this is the case that I've xtrfm in every electrical room but no access to get a qualify electrode because there is no way to bond the steel.

 

[marcosgue]

I'm talking about metallic joist that are bolted and welded and in some spots have continuity with steel columns down to earth and others no. the roof is composed with metallic decking at the top of the joist

 

[hillbilly1]

At one time building steel was acceptable as a GEC, but changed a while back when it had to be connected to the rebar in the slab before it could be considered a GEC. You are talking about the steel roof trusses? Not an actual steel roof?

 

[marcosgue]

yes, like a roof truss

 

[marcosgue]

some roof areas are composed by trusses as final terminations and some of this elements have continuity to earth through the columns

 

[Another C10]

without reading all the great comments above, I'd say The primary grounding path of any circuit needs to go back to the utility return, neutral conductor. The earth electrode ground is really for additional protection in case of lighting strikes, the bonding of metallic structures water lines or even gas lines is simply to reassure that entire building has the same path back to the main switchgear where everything originates.
That's how I've understood it ..

 

[marcosgue]

in grounded system one of the main function of the grounding electrode is limit the voltage to ground in case of some disturbance due to lightning strike like you say, and others causes and stabilizes the voltage to ground in the electrical supply, service or SDS, which is the case without any accesible grounding electrode, metal water pipe, building steel, cee, if is possible may use this metallic roof or use ground rod or ground ring instead?

 

[roger]

As already stated, the metal framing can be used but only if it meets the qualifications of 250.52(A)(2), the decking or roof panels would not be acceptable.

Driving rods as you suggested (or any other GEC listed in 250.52) would also be acceptable if the metal framing does not meet 250.52(A)

Roger

 

[Dennis Alwon]

The problem with the steel is proving that it is an electrode. I assume this is an existing building...or is it new? If new then the steel should have been connected to the grounding electrode system usually near the service

Metal In-ground Support Structure(s). One or more metal
in-ground support structure(s) in direct contact with the earth
vertically for 3.0 m (10 ft) or more, with or without concrete
encasement. If multiple metal in-ground support structures are
present at a building or a structure, it shall be permissible to
bond only one into the grounding electrode system

 

[marcosgue]

it's new construction Dennis, but they poor the footing, slab, steel columns without bonding anything's to the grounding electrode system and now they want use the metallic structure of the roof like only steel accesible and bond the X0 in every SDS and I disagree because the roof that's not qualify as electrode according to 250.52.

 

[don_resqcapt19]

yes, the roof is bonded thru the steel columns, however there's no grounding electrode (CEE, metal water pipe,) accessible to electrical room to bond the grounding electrode system and the SDS and someone says bond to the roof is acceptable, I believe this's not correct.
this would be an acceptable method in this specific situation?

If any of the grounding electrodes in 250.52(A)(1) through (A)(7) are present at the building they must be used. How accessible those electrodes are to the electrical room does not matter.