NEC 2011 Drywall a grounded or non grounded surface

[Dennis Alwon]

"Grounded" in this context has nothing to do with Mother Earth. Instead, ask this question: Does it form a low impedence path back to the transformer that 'made' the electricity?

And how would the wall have an impedance? It would have to connected to earth somehow - perhaps not electrically- but it would have to have some connection to have a lower impedance. The only wall I could see a sheetrock wall have SOME impedance is if there were metal studs and the screws for the sheetrock were visible otherwise I doubt it would be conductive.

 

[GoldDigger]

And how would the wall have an impedance? It would have to connected to earth somehow - perhaps not electrically- but it would have to have some connection to have a lower impedance. The only wall I could see a sheetrock wall have SOME impedance is if there were metal studs and the screws for the sheetrock were visible otherwise I doubt it would be conductive.

Except when you are rewiring a building after a flood.....

 

[charlie b]

Perhaps I have had no technical basis for this, but I have always treated a drywall surface as "grounded," in the context of 110.26 and 110.34. If I am laying out a room that has sheetrock on the walls (not often does this happen in electrical rooms, but sometimes in corridors), then I provide clearance space for Condition 2. But then, if I were an Inspector and if the engineer or EC only provided clearance space for Condition 1, I would be hard pressed to justify failing the installation. I suppose if the studs were metal and the drywall was attached using metal screws that are now hidden by a thin layer of drywall patch, I could say that an electrical hazard does exist.

 

[charlie b]

And how would the wall have an impedance? It would have to connected to earth somehow. . .

Everything has impedance; everything is connected (electrically) to planet Earth. There is a value of impedance between the kitchen countertop in your house and the sheetrock wall in my dining room, just as there is a value of capacitance between the watch on your wrist and the ring on my right hand. The numbers are ridiculously high and low perhaps (in that order), but they are very real parameters. The question at hand is how high, or low, the impedance of a sheetrock wall is, and whether it is low enough to create an electrical shock hazard.

 

[GoldDigger]

The question at hand is how high, or low, the impedance of a sheetrock wall is, and whether it is low enough to create an electrical shock hazard.

And an additional critical component is the extent to which that impedance is dependent on factors such as applied voltage, humidity level, etc.
The example of grounded screw heads thinly covered with drywall mud and/or paint is one which is highly dependent on the applied voltage, and also sensitive to mechanical damage.

 

[Dennis Alwon]

Everything has impedance; everything is connected (electrically) to planet Earth. There is a value of impedance between the kitchen countertop in your house and the sheetrock wall in my dining room, just as there is a value of capacitance between the watch on your wrist and the ring on my right hand. The numbers are ridiculously high and low perhaps (in that order), but they are very real parameters. The question at hand is how high, or low, the impedance of a sheetrock wall is, and whether it is low enough to create an electrical shock hazard.

Yes I realize that. I should have said how would a sheetrock wall has an impedance that would be dangerous if in contact with it and a mv cable or reg. voltage cable