300.5 question

[LarryFine]

I'm going to run a 30a 120/240 feeder to a shed in a residential back yard, and Table 300.5 is a bit confusing. It seems to say that under a residential driveway requires 18", while not under a driveway requires 24", but what if the driveway is gravel? Are RMC or 2" of concrete the only shallower alternatives? This install happens to be under gravel, but not really a driveway.

 

[Dennis Alwon]

A driveway is a driveway whether it is paved or not per the nec. The only alternative to a shallower grave is gfci protection or rmc...afaik

 

[Dennis Alwon]

Even if it isn't a driveway unless it is gfci protected the nm must be 24"...

 

[packersparky]

I'm going to run a 30a 120/240 feeder to a shed in a residential back yard, and Table 300.5 is a bit confusing. It seems to say that under a residential driveway requires 18", while not under a driveway requires 24", but what if the driveway is gravel? Are RMC or 2" of concrete the only shallower alternatives? This install happens to be under gravel, but not really a driveway.

If you use PVC, the minimum depth is 18 inches per Column 3.

 

[jumper]

Larry, I have asked this same question and read similar threads on the subject.

Yeah, it is screwy. The NEC does not say that the driveway has to be paved nor define just what is a driveway or parking area.

Heck most suburban and rural yards could be considered parking areas.

The best answer I ever saw so far was from Charlie E. Remember him, guy in Indy and former mod?

Anyways, the idea was that people may be less inclined to be digging up a driveway and thus damaging the cables.

Seems reasonable. Who plants a tree in the middle of the drive?

Best I can come up with.

 

[LarryFine]

Question 2: Would you guys select 1/2" RMC at 6" over PVC at 18" for, say, a 25' to 30' run? Consider we are crossing an underground service lateral and cable-TV run using a trencher we'd have to rent in the answer.

Added: The savings in the cost difference between a 12" and 24" trencher rental is more than enough to cover the cost of the conduit and fittings. Does the presence of gravel automatically mean the area must be a driveway?

 

[jumper]

Question 2: Would you guys select 1/2" RMC at 6" over PVC at 18" for, say, a 25' to 30' run? Consider we are crossing an underground service lateral and cable-TV run using a trencher we'd have to rent in the answer.

At about 12-13$ a stick. Yes, RMC, no trencher. You could use a rototiller for 6” depth.

 

[LarryFine]

Even if it isn't a driveway unless it is gfci protected the nm must be 24"...

That exception only applies to a 120v max 20a max circuit.

 

[LarryFine]

So, as I look over the table more, a cable run through a residential yard is required to be 24" deep, and not 18"?

 

[packersparky]

So, as I look over the table more, a cable run through a residential yard is required to be 24" deep, and not 18"?

That's the way I see it for a direct burial cable.

 

[jumper]

So, as I look over the table more, a cable run through a residential yard is required to be 24" deep, and not 18"?

Yes.

But only 18” under a resi driveway. Counter intuitive isn’t it?

 

[JFletcher]

With that distance, I'd go 6" with the RMC. Seems any time I trench deeper, I hit something not good, usually unmentioned automatic sprinkler control wires/plumbing. Even if you dont hit anything, there is less backfilling and less disturbance to the lawn. and for 25-30', unless it's solid rock, you can dig that by hand before you'd get to the rental store and back with a trencher, unload, trench, reload and take back to the rental place.

 

[LarryFine]

"Captain Kirk, I shall consider it!" - Spock with a beard in Mirror, Mirror