EMT encased in concrete

[infinity]

I have several floor boxes chopped into an existing concrete floor, fed with a 3" deep trench that contains (2) 3/4" EMT conduits. Is there a minimum requirement for how much concrete must be covering the conduit?

 

[Tom.Margillo]

Re: EMT encased in concrete

I would have to say you could cover it with as much or as little concrete as you want because the EMT wont be there for long. Use PVC, I beleive you need 2" of cover on that.

 

[iwire]

Re: EMT encased in concrete

Originally posted by infinity:
I have several floor boxes chopped into an existing concrete floor, fed with a 3" deep trench that contains (2) 3/4" EMT conduits. Is there a minimum requirement for how much concrete must be covering the conduit?

I think this section may be on the mark.

300.4(E) Cables and Raceways Installed in Shallow Grooves. Cable- or raceway-type wiring methods installed in a groove, to be covered by wallboard, siding, paneling, carpeting, or similar finish, shall be protected by 1.6 mm (1/16 in.) thick steel plate, sleeve, or equivalent or by not less than 32 mm (11/4 in.) free space for the full length of the groove in which the cable or raceway is installed.

Exception: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.

I would say your EMT could be flush with the surface or any distance below that.

Originally posted by Tom.Margillo:
I would have to say you could cover it with as much or as little concrete as you want because the EMT wont be there for long. Use PVC, I beleive you need 2" of cover on that.

I would have run PVC also however UL considers EMT OK for concrete encasement in many locations here is some info.

2004 UL White Book
ELECTRICAL METALLIC TUBING
(FJMX)

Galvanized steel electrical metallic tubing installed in concrete on grade or above generally requires no supplementary corrosion protection.

Galvanized steel electrical metallic tubing in concrete slab below grade level may require supplementary corrosion protection.

[ June 18, 2005, 08:20 AM: Message edited by: iwire ]

 

[infinity]

Re: EMT encased in concrete

Thanks for the responses. I was having a discussion the other day and a fellow electrician stated that the EMT needed to be under a minimum of 2" of concrete. I disagreed and he couldn't provide a code section to back it up.

Regarding 300.4(E), IMO, this would not apply to the installation I mentioned in my original post. Concrete encasement isn't a covering by wallboard, siding, paneling, carpeting, or similar finish.

 

[iwire]

Re: EMT encased in concrete

Originally posted by infinity:
Regarding 300.4(E), IMO, this would not apply to the installation I mentioned in my original post. Concrete encasement isn't a covering by wallboard, siding, paneling, carpeting, or similar finish.

Well then I find nothing to guide you as EMT in a cement slab is not underground so 300.5 is out.

My point with 300.4(E) is that it shows the NECs acceptance of EMT covered but just under the surface when not an underground installation.

 

[hardworkingstiff]

Re: EMT encased in concrete

Originally posted by infinity:
I was having a discussion the other day and a fellow electrician stated that the EMT needed to be under a minimum of 2" of concrete. I disagreed and he couldn't provide a code section to back it up.

I think that is just an old standard. I remember hearing that back in the early 70's.

 

[charlie]

Re: EMT encased in concrete

Don't forget, if the Code doesn't say you can't then you can.

 

[marinesgt0411]

Re: EMT encased in concrete

358.12(3)

358.12 uses not permitted

358.12(3)In cinder concrete or cinder fill where subject to permanent moisture unless protected on al sides by a layer of noncinder concrete at least 50 mm (2 in) thick or unless the tubing is at least 450 mm (18 in)under the fill

also 358.10 uses permitted

allow EMT in concrete

So if I read this correctly you can put EMT in concrete, if it is inside not subject to moisture it does not need corrosion protection, it can be at any depth as long as it is not cinder concrete and if it is it has to have 2 inches of non-cinder concrete all around it.

 

[cselectric]

Re: EMT encased in concrete

Originally posted by charlie:
Don't forget, if the Code doesn't say you can't then you can.

Ahh yes, Number one on the list of lifes unwritten rules: "that which is not expressly prohibited shall be allowed."

 

[tom baker]

Re: EMT encased in concrete

Keep in mind local codes may not allow encasing EMT in concrete, in Washington State we can not encase EMT in concrete.