EMT under slab

[tyha]

can EMT be installed under a slab on grade below the gravel and vapor barrier?

 

[raider1]

Take a look at 358.10(B) and 358.12(2).

Chris

 

[iMuse97]

According to some, you can protect from corrosion under the slab and vapor barrier.

In my experience, unless you've got some magic protection material, your EMT installation will last at most 30-40 years before the lowest spots in the pipe will corrode completely through, and be filled with oxidized metal, dirt, etc. I would install heavywall, with pvc coating, or if you are working in resi. avoid it altogether, or install PVC anywhere below the slab.

 

[tyha]

I know the code articles and that is what I am having trouble with. It has similar language for installing outdoors. Is EMT corrosion protected material. Even when you look at 300.6 (3) Im comming up with the same question. Has anyone ever done this before. I remember years ago in a mall we did it, I think we taped the couplings though. This was 20 years or so ago.

 

[cowboyjwc]

All I have to say is, drive a piece of EMT into the ground and see how long the end that's in the ground lasts.

 

[don_resqcapt19]

From the UL Guide for EMT (FJMX).

In general, galvanized steel electrical metallic tubing in contact with soil requires supplementary corrosion protection. Where galvanized steel electrical metallic tubing without supplementary corrosion protection extends directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil.

From the UL Guide for ferrous rigid conduit (DYIX).

Galvanized rigid steel conduit installed in contact with soil does not generally require supplementary corrosion protection.

 

[LJSMITH1]

EMT "Installation Outdoors" and "Direct Burial" are two completely different things. Also, "Direct Contact with Earth" is not identical in meaning with "Direct Burial".

As Raider already indicated, 358.10(B) and 358.12(2) are the requirements. EMT should not be directly buried in soil without some kind of supplementary corrosion protection (i.e. PVC coating, plastic sheath, asphalt compound, etc.). In the highlighted note section directly below 358.10(C) it states:

"The UL WhiteBook, Category FJMX, states that in general, galvanized steel EMT in contact with soil requires supplementary corrosion protection. Where galvanized steel EMT without supplementary corrosion protection extends directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil."

Also the FPN states to see 300.6 for protection against corrosion - which references the methods I stated in my 2nd paragraph.

Also, taping couplings will do nothing to prevent the intrusion of water into the conduit. The practice of taping fittings is only designed to prevent concrete aggregate from entering the raceway, not water.

 

[LJSMITH1]

Don typed faster than I did!:grin: I need to put down the sandwich...

 

[Pierre C Belarge]

Don typed faster than I did!:grin: I need to put down the sandwich...

or
Hold the sandwich in your mouth next time. :grin:

 

[Power Tech]

Ground level no. High rise, 2nd floor and above, yes.

Rain tight connectors and couplings.

 

[infinity]

Ground level no. High rise, 2nd floor and above, yes.

Rain tight connectors and couplings.

Wouldn't that be concrete tight fittings if installed in concrete? I've seen set screw fitting that are concrete tight when taped.