burial depth under concrete driveway

[Stevenfyeager]

Under concrete residential driveway, 12" depth required for GFCI protected, 20 amp, correct ? Does this 12" include the 4" of concrete ? Thank you.

 

[Stevenfyeager]

Under concrete residential driveway, 12" depth required for GFCI protected, 20 amp, correct ? Does this 12" include the 4" of concrete ? Thank you.

Or do I use the second row of 300.5, below concrete, depth of 6 " ?

 

[kwired]

Under concrete residential driveway, 12" depth required for GFCI protected, 20 amp, correct ? Does this 12" include the 4" of concrete ? Thank you.

Or do I use the second row of 300.5, below concrete, depth of 6 " ?

I think it is from surface of driveway, but it really doesn't say either.

second row is for "other than driveway" slabs, no vehicular traffic.

 

[Buck Parrish]

From the table's notes.

Notes:

1. Cover is defined as the shortest distance in millimeters (inches) measured between a point on the top surface of any direct-buried conductor, cable, conduit, or other raceway and the top surface of finished grade, concrete, or similar cover.

 

[MTW]

I always put mine below the frost line, once and done.

 

[Stevenfyeager]

I think it is from surface of driveway, but it really doesn't say either.

second row is for "other than driveway" slabs, no vehicular traffic.

Thanks, but the second row in 2017 NEC I was looking at just says below (2”) concrete It doesn’t say anything about traffic. 6” Am I wrong to use this row ?
The dwelling driveway row doesn’t mention concrete, so does the concrete row (2nd row) change it to 6”? Thank you.

 

[wwhitney]

second row is for "other than driveway" slabs, no vehicular traffic.

Except it doesn't say that. Nothing specifies how to handle the situation that more than one row applies, whether to take the lesser or greater depth. If the second row also included the "not specified below" language, then it would avoid that ambiguity.

The conservative choice is to take the larger depth. And Note 4, which covers the case of multiple columns applying simultaneously, indirectly suggests that the larger depth is intended to be the default choice, in that Note 4 gives specific permission for the shallower depth.

But none of that is definitive.

Cheers, Wayne

 

[Barney B]

Table 300.5, Column 4, Line 6, very specifically covers this case. "One- and two-family dwelling driveway...residential branch circuits rated 120V or less...GFCI protection...max OCPD 20A...12 inches". The concrete thickness is part of the required cover (see Note 1).

 

[wwhitney]

Table 300.5, Column 4, Line 6, very specifically covers this case. "One- and two-family dwelling driveway."

Yes, but if the driveway is made of concrete, then the Line 2 description also covers the installation.

Cheers, Wayne

 

[infinity]

Table 300.5, Column 4, Line 6, very specifically covers this case. "One- and two-family dwelling driveway...residential branch circuits rated 120V or less...GFCI protection...max OCPD 20A...12 inches". The concrete thickness is part of the required cover (see Note 1).

I agree. A concrete driveway changes nothing.

 

[mtnelect]

Undergrounding electrical circuits.

 

[wwhitney]

I agree. A concrete driveway changes nothing.

Other than introducing ambiguity as to which row applies. Although the choosing the greater depth is obviously conservative.

Cheers, Wayne

 

[petersonra]

Other than introducing ambiguity as to which row applies. Although the choosing the greater depth is obviously conservative.

Cheers, Wayne

One might think that a suggestion to remove the ambiguity is in order. But the CMP would probably claim there is no ambiguity.

 

[infinity]

One might think that a suggestion to remove the ambiguity is in order. But the CMP would probably claim there is no ambiguity.

I don't see any ambiguity either. It's under a driveway and a one or two family dwelling so that's the line that applies.

 

[wwhitney]

I don't see any ambiguity either. It's under a driveway and a one or two family dwelling so that's the line that applies.

But it's under 2" of concrete, so that's the line that applies.

Wayne

 

[petersonra]

But it's under 2" of concrete, so that's the line that applies.

Wayne

how do you know the concrete driveway is 2" thick?

 

[wwhitney]

how do you know the concrete driveway is 2" thick?

Obviously an assumption, but it's going to be true for 99.9% of concrete slabs on grade. I guess if you had a perfectly compacted stable subbase with no moisture related movement of any kind, you might be able to drive on a 1-1/2" thick slab and it would hold up. But even most sidewalks are at least 2".

Anyway, if the new circuit is going in from above, then just put at least 2" of concrete back in when you patch it. And if it's being horizontally bored from the side, that should reveal how thick the concrete is, at least at the edge.

Cheers, Wayne

 

[petersonra]

also, how do you know it is in a trench under the driveway.

 

[wwhitney]

also, how do you know it is in a trench under the driveway.

I don't ascribe any content to those words. I don't believe it is attempting to specify the installation method, rather than just the final result.

Cheers, Wayne

 

[petersonra]

Line 2 specifically says:

In trench below 50 mm (2 in.)
thick concrete or equivalent

So if it is not in a trench you can't use that line.