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#88558 - 06/26/04 11:19 AM conduits in concrete floor slabs  
JBO1960  Offline
Junior Member
Joined: Jun 2004
Posts: 2
Upton, NY, USA
What is the minimum concrete coverage for conduits/raceways installed in building floor slabs and where is it referenced in the NEC.


James Wright
Project Enginner I

2017 / 2014 NEC & Related Books and Study Guides

#88559 - 06/26/04 12:58 PM Re: conduits in concrete floor slabs  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
0"

Table 300.5


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#88560 - 06/26/04 09:05 PM Re: conduits in concrete floor slabs  
trekkie76  Offline
Member
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
2" according to t300-5 note #2
" raceways approved for burial only where concrete encased shallrequire concrete envelope not less than 2" "


#88561 - 06/26/04 10:12 PM Re: conduits in concrete floor slabs  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Trekkie, That note only applies to raceways that are only approved for direct burial with concrete encasement.

That note does not apply to RMC, RNC, IMC etc. Those methods can be direct buried without the need of concrete, those methods only need 0" of cover under a building. [Linked Image]

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#88562 - 06/27/04 06:25 PM Re: conduits in concrete floor slabs  
trekkie76  Offline
Member
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
I always thought the 0" meant that the wiring method could't be used in the particular situation. What is considered " under a building"? we are talking about in a slab not under it. wouldn't that be all other locations?


#88563 - 06/28/04 03:06 PM Re: conduits in concrete floor slabs  
JBO1960  Offline
Junior Member
Joined: Jun 2004
Posts: 2
Upton, NY, USA
It is my understanding that Article 300.5 "Underground Installations" and Table 300.5 was specifically for conduits installed underground or under slabs. No where does the code state for conduits installed "within" floor/ceiling slabs. If you are refering to table 300.5, "All locations not specified below" then for RGS would need to have 6" cover in a slab.
This cant be right.


James Wright
Project Enginner I

#88564 - 06/28/04 08:15 PM Re: conduits in concrete floor slabs  
Nick  Offline
Member
Joined: Aug 2001
Posts: 599
Riverside, CA
OK how about 300.6(B). There is no cover requirement but it does specifically allow suitable raceways "in" concrete.


#88565 - 06/29/04 05:16 PM Re: conduits in concrete floor slabs  
earlydean  Offline
Member
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
The building code (2003 IBC) has this to say:
"1906.3 Conduits and pipes embedded in concrete.
Conduits, pipes and sleeves of any material not harmful to concrete and within the limitations of ACI 318, Section 6.3, are permitted to be embedded in concrete with approval of the registered design professional."

And, generally the cover requirements are the same as for rebar:

TABLE 1907.7.1
MINIMUM CONCRETE COVER

CONCRETE EXPOSURE MINIMUM COVER
1.Concrete cast against and permanently exposed to earth 3"

2.Concrete exposed to earth or weather
No. 6 through No. 18 bar 2"
No. 5 bar, W31 or D31 wire, and smaller 1½"

3.Concrete not exposed to weather or in contact with ground
Slabs, walls, joists:
No. 14 and No. 18 bars 1½"
No. 11 bar and smaller ¾"
Beams, columns:
Primary reinforcement, ties, stirrups, spirals Shells, folded plate members: 1½"
No. 6 bar and larger ¾"
No. 5 bar, W31 or D31 wire, and smaller ½"

Engineers and concrete contractors look at embedded conduit as a necessary evil. Conduit doesn't provide much in the way of strength and can often weaken the concrete if not installed correctly. Keep your embedded conduit runs at least 2 inches back (or structural engineer's requirements) from the finish to avoid "pop-outs", and allow space between the conduit and the rebar for the aggragate to flow all around both. If installing in floor slabs, install the conduit under the wire mesh.


Earl


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