UF burial depth and table 300.5 confusion

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sbrehler

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Hey all,

I am working on a project that involves running a couple of GFCI protected circuits (1-15A, 1- 20A) and 3-15A switch-legs (non-GFCI) over to a carport (it is continuous to the house connected by a breezeway). The previous electricians ran the switch-legs into the crawlspace during the home renovation a couple of years ago anticipating this project (they are no longer in the picture). I am going to run UF from the house crawlspace over to the carport and into a 2" turn-up into the carport foundation. The GC had the masons install the turn-up at a depth of about 24" but only trenched out a couple of feet when the project started. The thinking was that the GC would dig the trench later and we would connect at that time. Trouble is, they trenched down and ran into the old drive way at about 16-18". We are now trying to see if I can make the connection without having to break through the old driveway...

When looking at table 300.5 I am seeing that I can't use column 4 due to the switch legs not being GFCI protected. Going to table 1, I see that for direct burial cable that if it is for "one- and two-family dwelling driveways and outdoor parking areas, and used only for dwelling-related purposes" that I can lay it in at the 18" (that we can probably get away with). The confusion is that the trench is not part of a driveway or parking area. It is just a small grassy area between the house and carport. Does this mean I have to go with the "All locations not specified below" row and bury it at 24"? Which, will mean breaking up the old drive! I'm not sure how to apply this...

Any input would be appreciated...

Scott
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Directional boring under the old driveway? Just how thick is it?
You would need to drop the trench lower on either side of the driveway to connect.
 

iwire

Moderator
Staff member
Location
Massachusetts
In my opinion yes 24"

I would likely run, in fact I know I would run PVC which is fine at 18" the entire way.


However I think you have bigger problems,


running a couple of GFCI protected circuits (1-15A, 1- 20A)


you can only run one branch circuit to a separate structure. See part II of article 225. There are exceptions for the switchlegs but not for the 15 & 20 amp circuits.
 

sbrehler

Member
In my opinion yes 24"

I would likely run, in fact I know I would run PVC which is fine at 18" the entire way.


However I think you have bigger problems,





you can only run one branch circuit to a separate structure. See part II of article 225. There are exceptions for the switchlegs but not for the 15 & 20 amp circuits.

What is confusing to me is why would one be able to run the cables under a driveway at 18", but not elsewhere? Why are residential driveways and parking spaces given depth that, as I see it, a more threatening condition that say under a grassy yard that the table makes one default to a greater depth?

I was going to run the PVC, but the way the stub-up into the carport is I would have to add a couple more 90's to get it above the drive. That would involve busting a little of the concrete out, but my bigger concern is pulling the 5 cables through 270 degrees of bends. I could probably do it, but I would most likely be a PITA! But, yes, probably better than busting the concrete.

Re: the separate structure. As I mentioned, they are contiguous roof lines connected by a breeze way. I believe that makes them "one."

Thanks for your thoughts...
 

sbrehler

Member
Directional boring under the old driveway? Just how thick is it?
You would need to drop the trench lower on either side of the driveway to connect.

Im afraid the the way the buildings are already situated, that that isn't an option...

Thanks for the idea!
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Scott, run pvc and go down 18" or go 6" and use galvanized pipe.

I agree this is not a separate structure from the way you described it
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Would it be compliant to sleeve the section at 18" depth with PVC and still direct bury the rest of the UF at 24"?

Cheers, Wayne
 

kwired

Electron manager
Location
NE Nebraska
What is confusing to me is why would one be able to run the cables under a driveway at 18", but not elsewhere? Why are residential driveways and parking spaces given depth that, as I see it, a more threatening condition that say under a grassy yard that the table makes one default to a greater depth?

Take a shovel and try to dig up the portion under the driveway and then try to did up the portion in the grassy yard and tell us which was easier to access.;)
 

sbrehler

Member
Take a shovel and try to dig up the portion under the driveway and then try to did up the portion in the grassy yard and tell us which was easier to access.;)
Point taken. I had thought of that, but also wondered how a cable buried in a location where people wouldn't necessarily dig but have a 3-6 ton vehicle drive over/on top of would allow a shallower burial depth that "All locations not specified..."? :?

Thanks everybody for your input. I looks like the GC will be busting up some concrete...
 

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
rather than busting up concrete, do you have access to a 4 GPM, 4000 psi pressure washer or similar? And a sump pump if the soil does not drain very well?

I've 'carved' a 3-4" hole about 9 feet under concrete walks and drives with pressure washer with a piece of pipe as extension wand. And that was in soil with cobble in it, easier in other non-rocky soil types.

The POCO here even digs holes around power lines now with a pressure washer and big vacuum truck, no shovels or backhoe to damage existing lines.
 
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