Trench Depth For Conduit Under 4" Concrete Slab

[3oFElectric]

If I've got Schedule 40 PVC conduit stubbing up through 4" of concrete slab in single family dwelling, would I be required to trench 12" below the slab per Table 300.5, Column 3, Line 2 even though slab is 4" rather than 2" thick?

 

[roger]

Why would you think 4" would be less protection than 2"?

 

[3oFElectric]

Actually I'm thinking the opposite. I'd think 4" is more protection and thus wouldn't require me to trench 12" below it because it's thicker than the 2" specified in Table 300.5.

 

[roger]

Actually I'm thinking the opposite. I'd think 4" is more protection and thus wouldn't require me to trench 12" below it because it's thicker than the 2" specified in Table 300.5.

Correct.

 

[3oFElectric]

Correct.

Perfect. Thanks for the clarification. How much depth should I then trench given I'm under 4" slab? Would I deduct 2" from my required depth and go only 10"?

 

[infinity]

If it's under the slab isn't it under the building requiring 0" of burial depth?

 

[3oFElectric]

I see that under Line 3 of Table 300.5. Would that be if the conduit passes beneath a building or if I stub up into the building? I'd definitely prefer 0" burial depth. But want to be sure of the code requirement in this situation before I start laying down conduit.

 

[infinity]

I see that under Line 3 of Table 300.5. Would that be if the conduit passes beneath a building or if I stub up into the building? I'd definitely prefer 0" burial depth. But want to be sure of the code requirement in this situation before I start laying down conduit.

IMO it's under the building but I'll wait to hear other opinions.

 

[roger]

IMO it's under the building but I'll wait to hear other opinions.

Agreed, it's under the building and outside per 230.6

 

[Fred B]

Under the building with 4 in of concrete and a 4 inch pipe your trench would only be the depth of the pipe, cover would be 0 in. Outside of building it seem it would be min trench of 12 inch with 4 inch pipe 4 inch of cover and 4 inch of concrete. as long as no vehicle traffic.