damp or wet location

[patriot]

Is a concrete slab a wet location? I know what the nec definition says. Is it saying only a slab that is in contact with earth or any slab at all? To me it reads any slab at all but we were talking about it at work and every one seemed to think I was interpriting it wrong. A little feedback on this would be greatly appriciated. Theres a cold drink on the line here.lol

 

[dana1028]

The definition for wet location says, "concrete slabs...in direct contact with the earth."

 

[cadpoint]

Seems I recall that by the Code it mentions that direct concrete to earth and no poly-liner, required when grounding. A Slab cures over 20 years what or where is the "Slab". And "AIR" there is no Code to go back and address the a "slab".

Wet and Dry would get into a called out "Area" or to be such, "Titled" or would get into Building Codes per the space, or even Flood Plain Maps!

 

[Dennis Alwon]

I agree with Dana although the way the definition is written is a bit vague-- it could be read as any slab but I don't believe that is what it means. Direct contact with earth then it is wet location. Obviously a second floor slab would not be in contact with the earth- dry location, IMO.

 

[infinity]

I agree with Dana although the way the definition is written is a bit vague-- it could be read as any slab but I don't believe that is what it means. Direct contact with earth then it is wet location. Obviously a second floor slab would not be in contact with the earth- dry location, IMO.

I concur and this is to clarify that, for instance, a conduit run out to a kitchen island, in slab and on grade cannot contain NM cable.

 

[G._S._Ohm]

And the resistivity of dry concrete is way higher than that of wet concrete, soil or fresh water.

 

[Dennis Alwon]

And the resistivity of dry concrete is way higher than that of wet concrete, soil or fresh water.

What has that to do with the classification of wet or dry location?

 

[G._S._Ohm]

What has that to do with the classification of wet or dry location?

A possible rationale for the classification and whether it applies to concrete that doesn't touch the ground.

 

[Dennis Alwon]

A possible rationale for the classification and whether it applies to concrete that doesn't touch the ground.

But what does resistivity of concrete have to do with needing a wire rated for wet location. The wire is in a conduit perhaps PVC so I don't get it.

 

[LarryFine]

The definition for wet location says, "concrete slabs...in direct contact with the earth."

Direct contact with earth then it is wet location. Obviously a second floor slab would not be in contact with the earth- dry location, IMO.

I've seen plenty of above-grade slab conduits that were quite wet.

And the resistivity of dry concrete is way higher than that of wet concrete, soil or fresh water.

It's my understanding that concrete is never truly dry. It certainly can cure without drying.

 

[dana1028]

I've seen plenty of above-grade slab conduits that were quite wet.

Larry - I agree with you, and as an electrician I would always install W rated conductors in any conduit run in concrete.

However, as an inspector, as you folks constantly point out, 'show it to me in the code.' I have to be able to show someone a code section, definition that will back up my mouth - by definition it appears slabs on grade are wet locations...it does not indicate slabs on the interior of the 2nd floor of a building is a wet location.

The bright side - usually this type of work is done by commercial electricians, who pull the double rated THHN/THWN wire through conduit and don't use NM cable or none 'W' rated wire....so this is rarely an issue on the job site. If fact, I don't recall ever seeing this being a problem on a job site.

 

[Dennis Alwon]

The bright side - usually this type of work is done by commercial electricians, who pull the double rated THHN/THWN wire through conduit and don't use NM cable or none 'W' rated wire....so this is rarely an issue on the job site. If fact, I don't recall ever seeing this being a problem on a job site.

I agree. I disagree that conduit above grade in a slab indoors is likely to have water. Heck you can have some condensation almost anywhere but a slab will pretty much dry out in conditioned environment, IMO

 

[G._S._Ohm]

But what does resistivity of concrete have to do with needing a wire rated for wet location. The wire is in a conduit perhaps PVC so I don't get it.

The OP didn't mention a wire. Maybe I should have read that into it.