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Depth of Conduit Beneath Residential Garage Slab

jar546

jar546

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Oct 16, 2009
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Not where I really want to be
If there is an electrical meter on a residential, detached garage AND the electrician needs to put the main service panel on the opposite side of the garage in order to comply with the owner's wishes,..how deep must his PVC conduit for this installation be where it goes under the proposed slab for the garage?
Clarifications:
1) These are considered service conductors.
2) Would your opinion change if the conduit was for a feeder.
 
Yea, hate to be the oddball here, but IRC Table 3803.1, column 3, row 1, all locations not specified below. 18". I would not consider this under a building. You don't generally drive vehicles in buildings, and comparatively, vehicular traffic is a mediating factor. This is for service conductors or feeders.
 
rgrace said:
IRC Table 3803.1, column 3, row 1, all locations not specified below. 18". I would not consider this under a building. You don't generally drive vehicles in buildings, and comparatively, vehicular traffic is a mediating factor. This is for service conductors or feeders.
Click to expand...

Header Column 3 sez, without concrete encasement. Would a 4-inch slab act as the encasement? (pad of concrete over conduit) *Did not find a definition in the NEC for encasement.

Assumed the proposed concrete slab is a 4-inch concrete slab, see footnotes at bottom of table 3803.1
 
I take "encasement" as being within the concrete itself. Footnote a refers to a "concrete envelope" which I think supports this. Standard dictionary version "to enclose in."

Row 2 says "below" 2" concrete. Row 4 says "under" 4" concrete.

PVC can be installed direct burial or under-ground encased in concrete. NEC 352.10(G)

NEC also has a definition of "building - a structure that stands alone"

Brain hurts now. Have to rethink this. All references to vehicular is exterior. Building definition fits "detached garage." JCraver, doesn't look like I can help with the tax man :(
 
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Not that I haven't ever been wrong but I have always presumed the 2" was the min. cover if encased in concrete and if less than 18" it would need to be encased, Not a NEC genius though.:)
 
NEC Table 300.5, (under a building) Column #3 sez ZERO.

Different subject matter added by:
mark handler said:
If it's placed outside under a concrete slab,(driveway) then the minimum cover is 4 inches [Table 300.5].
Click to expand...

Column 3:
No vehicular traffic: 4" thick driveway
One and Two-family driveways: 18-inch
 
Here's my take on it, the difference between "outdoor" parking and driveways is the likely hood of digging through these areas to a depth is the potential for damage to the service cable is greater than under a building from inside. I suppose in accordance with 300.5(D)(3) there is the potential to use machinery to dig. As best practice, we used to test for underground cables with a shovel to a depth before using a backhoe.

When it's under a building I think we are likely to take precautions of where stuff such as service conductors, plumbing, gas, etc. is concealed or not exposed before using a hammer.

Feeders permitted in Article 340 and for approved conduits reference back to 300.5
 
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