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Dry Wall- Effectively Insulated or Grounded Wall?

Dry Wall- Effectively Insulated or Grounded Wall?

Dry Wall- Effectively Insulated or Grounded Wall?

(OP)
I have a 480V MCC that I am installing in electric room whose walls are composed of two layers of gypsum drywall.  I am using Table 110.26 in NEC to consider working space in front of the MCC.  In condition 2 of this Table, the code says to consider concrete, ceramic tile, and brick as grounded.  I am trying to determine if a drywall installation is "effectively insulated".  Can anyone point in the direction of how I can make this determination.  Thanks

RE: Dry Wall- Effectively Insulated or Grounded Wall?

Yep, grounded.  Put up a layer of 1/2 inch plywood and have an insulated surface.

RE: Dry Wall- Effectively Insulated or Grounded Wall?

I also can't see drywall qualifying as "effectively insulated". They often absorb moisture and can be conductive.

Rafiq Bulsara
http://www.srengineersct.com

RE: Dry Wall- Effectively Insulated or Grounded Wall?

Grounded.



 

RE: Dry Wall- Effectively Insulated or Grounded Wall?

(OP)
I will consider the wall as grounded.  What is interesting is that I couldn't find any documentation searching the internet for several hours that even touched on this issues. I thought of some testing that I could do with a megger on the installation.  Before doing the actual test, I megged at 1000Vdc a piece of drywall that I had in my garage (hot and humid).  The drywall tested over 2 giga-ohms with both probes firmly embedded in the sheetrock. It megged over 2 gigs with the probes being only inches apart! There was a couple of reasons that I didn't do any further testing.  One is that persons may invalidate the testing on the grounds that as you say conditions (moisture content) may change.  I don't think that in my case it will, but that it still a valid argument.  The other reason that I chose to call the drywall installation as grounded is that there are metal screws that attaches the dry wall to a metal stud frame.  The metal wall stud frame is attached to the building's metal steel frame which is attached the building's ground grid.

RE: Dry Wall- Effectively Insulated or Grounded Wall?

If you consider it ungrounded, you can reduce clearance by what - 6 inches.  No one will thank you for that.  If you consider it grounded, additional clearance is required, which is generally a good thing.  And you are covered if someone does something with the wall in the future that would increase its conductivity.  

 

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