Table 300.5

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Grouch1980

Grouch1980

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New York, NY
Hey all again!
On another project I'm on, they want to route RMC conduits along the 1st floor of a building. They will be buried under the surface of the 1st floor (there is no basement underneath). According to Table 300.5 in Article 300 (2008 NEC), I'm looking at Column 2 (Rigid Metal Conduit or Intermediate Metal Conduit), and the row i believe should be 'Under a building' (3rd row). Everything on that row is 0" minimum cover.

My 2 questions are:
1. Am i looking at the correct row for this application, 'under a building'?
2. By 0" minimum cover, the conduits can theoretically be right under the surface of the finished floor?

Thanks!
 
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I'm thinking 2" of concrete would suffice, but I wouldn't go zero. The floor will always have a crack there.
 
LarryFine said:
I'm thinking 2" of concrete would suffice, but I wouldn't go zero. The floor will always have a crack there.
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oh yeah, i wouldn't go to zero either... i'll probably ask for 1 foot depth. just wanted to know if i was reading the chart right... theoretically the depth of the conduits can be at 0". In other words, there is no minimum depth in this application.
 
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Unless that applies to under building floors as in crawl spaces that will see no traffic of any kind.
 
LarryFine said:
Unless that applies to under building floors as in crawl spaces that will see no traffic of any kind.
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that's why i'm not 100% sure if 'under a building' applies in my situation. the only other row that could apply is the 1st row: "All locations not specified below"... that places me at a minimum of 6" cover under Column 2.
 
Grouch1980 said:
that's why i'm not 100% sure if 'under a building' applies in my situation. the only other row that could apply is the 1st row: "All locations not specified below"... that places me at a minimum of 6" cover under Column 2.
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I almost said that, so I can't disagree with you.

However, only 2" of concrete is necessary to render a conduit as not inside a building.
 
I was pointing out that the 2" means a conduit is not inside, not that I thought it was a feeder requirement.

Therefor, a 2" concrete cover would mean the conduit is under the building, because it's not in the building.
 
welp, i follow up until post #6, and then i'm lost. The 2" concrete cover rendering a conduit not inside a building doesn't apply to me in this case, since these are not service conductors... do I have this correct?
 
Grouch1980 said:
welp, i follow up until post #6, and then i'm lost. The 2" concrete cover rendering a conduit not inside a building doesn't apply to me in this case, since these are not service conductors... do I have this correct?
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As a requirement, absolutely correct. There is no requirement that a feeder be either under a building nor under 2" of concrete.

I was merely suggesting that 2" of concrete is enough to be able claim it's under the building. It can't be both in and under it.
 
LarryFine said:
As a requirement, absolutely correct. There is no requirement that a feeder be either under a building nor under 2" of concrete.

I was merely suggesting that 2" of concrete is enough to be able claim it's under the building. It can't be both in and under it.
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ah ok. I'm following now, I see what you're getting at. ok, noted. I'm probably going as deep as 1 to 2 feet anyway. there may be plumbing pipes i have to avoid in the area as well.
 
Is the first floor poured concrete? If so you can put the conduit in the concrete where there is no minimum cover requirement so you can disregard T300.5 completely.
 
As Infinity said, also it could be PVC in the slab. Why do they want to pay the price for RMC in this day and age?
 
Strathead said:
As Infinity said, also it could be PVC in the slab. Why do they want to pay the price for RMC in this day and age?
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PVC may not be available (supply issue other threads are referencing), and if this is in NYC at one point PVC was not allowed, this may have changed IDK.
Another consideration, as soon as you go below grade/surface and qualifies to be considered outside of building, as Larry stated, the wire is considered to be in a wet/damp location and even if in conduit requires wiring suitable for such locations.
 
Fred B said:
Another consideration, as soon as you go below grade/surface and qualifies to be considered outside of building, as Larry stated, the wire is considered to be in a wet/damp location and even if in conduit requires wiring suitable for such locations.
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Definitely need wet-rated wire under a slab floor.
 
Hey guys!
So I confirmed a few things today with the architect. So the surface of the 1st floor will consist of a 4" concrete slab. under it will be the soil / backfill. There is no basement. So my conduits would be routed underneath this 4" concrete slab.

My questions now:
1. Does table 300.5 now apply? I do not think so.
2. Is there any depth requirement?
 
Grouch1980 said:
Hey guys!
So I confirmed a few things today with the architect. So the surface of the 1st floor will consist of a 4" concrete slab. under it will be the soil / backfill. There is no basement. So my conduits would be routed underneath this 4" concrete slab.

My questions now:
1. Does table 300.5 now apply? I do not think so.
2. Is there any depth requirement?
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If you are inside the perimeter walls of the building, there is no depth requirement. Some engineers will not permit the conduits in the concrete to avoid future cracking issues for the floor. We would typically put them in the fill so the top of the conduit is at or below the bottom of the concrete.
 
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