NEC 2011 Drywall a grounded or non grounded surface

[Markque]

In the 2011 National Electrical Code is drywall a grounded or non grounded surface for working clearances?

 

[Dennis Alwon]

I have no idea what you mean. Sheetrock is not a ground...

 

[Markque]

NEC 2011 Drywall a grounded or non grounded surface

In the 2011 NEC table 110.26(a)(1) condition 2 use to list drywall as a grounded surface, now it seems its silent on the issue.

 

[david luchini]

As 110.26(A)(1) Condition 2 describes "Concrete, brick and tile walls shall be considered as grounded," I would consider a sheetrock wall as non grounded.

 

[Dennis Alwon]

I have never seen that and I just read the 2008 and 2005 and there is no mention of sheetrock. What are you trying to figure out?

 

[david luchini]

In the 2011 NEC table 110.26(a)(1) condition 2 use to list drywall as a grounded surface, now it seems its silent on the issue.

What year did the NEC list drywall as a grounded surface in condition 2?

It looks like the "Concrete, brick or tile wall shall be considered as grounded" showed up in 1999. I don't see it in 87-96.

 

[Markque]

NEC 2011 Drywall a grounded or non grounded surface

Working clearances behind a MV 13.8 gear. I might have seen it in a hand book that the Inspector had.

 

[Markque]

NEC 2011 Drywall a grounded or non grounded surface

What's the test for a grounded vs. a non grounded surface. Resistance?

 

[Dennis Alwon]

It not in the MV table back to 2005. Anyway I wonder if you have tile on a sheetrock wall would that be considered grounded. It seems to say that since it is not specific.

 

[Markque]

NEC 2011 Drywall a grounded or non grounded surface

What is the test of a grounded surface.

 

[Dennis Alwon]

What is the test of a grounded surface.

I guess you can put a voltage tester on the wall and one side in a power source.

 

[GoldDigger]

I guess you can put a voltage tester on the wall and one side in a power source.

The resistivity of concrete is low enough that it can be used for a Concrete Encased Electrode (CEE). The same would generally apply to brick and to some but not all kinds of tile. The code is playing it safe by making the more general statement.

To get a good resistance indication you would have to have a large surface area, such as a metal or foil plate pressed against the wall.

Whether or not the surface is grounded will still depend on what the brick, concrete or tile are touching in the backing or at the edges. So the code is again being conservative and assuming that some part of the brick/tile/whatever structure is touching building steel, grounded concrete, or some other path to earth ground.

Dry wood or dry sheetrock, on the other hand, have a high enough resistance that there is no safety hazard. (But if you touch an exposed sheetrock screw that goes into a steel stud, you may be (figuratively) screwed just the same. )

 

[GoldDigger]

It not in the MV table back to 2005. Anyway I wonder if you have tile on a sheetrock wall would that be considered grounded. It seems to say that since it is not specific.

IMHO, it would not be grounded unless it touched something other than just the sheetrock. But verifying that it does not, especially if the tile goes all the way down to a concrete floor, for example, or if wire lath in the tile bed touches a screw penetrating the sheetrock, or if the grout or mastic is conductive. (I would not necessarily expect the drywall guys to mud over screws that will be covered by tile anyway, for example.)

If you can't see behind the tile, you can't trust it.

 

[rbalex]

Working clearances behind a MV 13.8 gear. I might have seen it in a hand book that the Inspector had.

Has anyone yet noted that Section 110.26 (A)(1) and its Table don?t apply to Medium Voltage switchgear; nor likely to the back of it?

While the ?Conditions? in Table 110.34(A) are the same, the ?back? of the switchgear is most likely covered by Section 110.34(A) Exception. It would be interesting to note whether the switchgear is metalclad or metal enclosed load interrupter type, in which case the ?Conditions? probably don?t matter.

 

[kwired]

Has anyone yet noted that Section 110.26 (A)(1) and its Table don?t apply to Medium Voltage switchgear; nor likely to the back of it?

Well I may have mentioned that but did not read this thread before you did.

110.34 doesn't mention drywall either, and did not mention it back in 2002, have not searched any further back because NEC plus only goes back that far.

I will say that many things that are non conductive below 600 volts are not necessarily considered non conductive above 600 volts.

Even POCO's that have both 2400 and 7200 to ground distribution systems will tell you the 7200 will usually end up tripping overcurrent protection if a tree grows into a line where a tree in the 2400 volt system sometimes will not, leaving a more hazardous situation in and around the tree.

 

[rbalex]

Actually, I was suggesting the rules on the rear of MV metalclad and load-interrupter gear are different.

 

[Blaer]

Here's how to tell:

Stand on an insulating mat. Grab a hot wire. Touch the drywall. If you survive, it's not grounded.

 

[eHunter]

Here's how to tell:

Stand on an insulating mat. Grab a hot wire. Touch the drywall. If you survive, it's not grounded.

Since this your idea, you test its validity and report back to us what the results are and you get to take the credit.

 

[GoldDigger]

I will say that many things that are non conductive below 600 volts are not necessarily considered non conductive above 600 volts.

Here's how to tell:
Stand on an insulating mat. Grab a hot wire. Touch the drywall. If you survive, it's not grounded.

So be sure to grab not just any old hot wire, but an MV wire. And, of course, use a very good insulating mat. :angel:

 

[Blaer]

Giggle all you want ... but isn't that the whole logic behind the distinction? Surfaces that make the shock worse are placed farther away; that's the clearance rule, all else is commentary.

"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?