UF-3, under cement, how deep?

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  #1  
Old 03-18-06, 02:25 PM
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UF-3, under cement, how deep?

I'm running UF underground to my garage. I know it's supposed to be 24" deep, but I am pouring 4" of concrete(driveway)up at grade level, over the UF, after I bury it in dirt. Do I really need to go that deep? What does code say about this. Can you tell me exactly in the 2005 NEC where I can read up on this? I just don't want to go 24" deep, if I don't have to, since I'm digging almost 50 feet of trench, by hand.
Thanks!
 
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Old 03-18-06, 02:49 PM
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Section 300.5 of the 2005 NEC discusses this.

Table 300.5 supplies the information you want, or in this case don;t want. It stipulates that under a driveway you must be 24 inches deep, regardless of what you run, UF or conduit.

For your installation, I recommend conduit, not UF. Conduit will make it much easier to replace the wire, should you ever need to do so.
 
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Old 03-18-06, 02:54 PM
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300.5 table say you can go 18" under driveway. for one and two family units
 
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Old 03-18-06, 02:59 PM
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Sorry, my bad. I didn;t read far enough down the table. 18 inches it is.
 
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Old 03-18-06, 04:57 PM
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Does that 18" have to be run in conduit, or can it be run with just the UF cable? I already know that I need sch 80 conduit on the verticle rise, and, above ground.
 
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Old 03-18-06, 05:10 PM
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#1 I would go with conduit, Sounds like a new house and you may want to be there for a while. Right? I know resurfacing is less expensive then re-doing. 50' $25-$30 1/2 day rental, get the machine. Do it once, do it right. You'll thank yourself later.
 
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Old 03-18-06, 06:22 PM
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Just read the 2005 Table 300.5, "Minimum Cover Requitements."

Direct burial cables for one-and two-family dwelling driveways, etc, 18"The notes below the table read, "Cover is defined as the shortest distance 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.



Therefore, I surmise that if the concrete sits 4" thick, above the grade level of the dirt, or if it sits 4" thick, with its top surface level with the grade of the dirt, in either case, I would only need to dig 14" of dirt below the bottom surface of the concrete, to meet the requirement of the total 18" of cover.

Any thoughts?
 
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Old 03-18-06, 09:10 PM
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check table 300.5 carefully and find all that apply, What voltage and amperage?

I would still go with conduit. (sorry)
 
  #9  
Old 03-18-06, 09:47 PM
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Is this a feeder or a branch circuit? The devil is in the details, and we need more of them.
 
  #10  
Old 03-19-06, 07:16 AM
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I'm feeding a 125 amp sub-panel in the garage.
It's about 50' from the main panel in the house.

How deep: Does the particular application(feeder or branch circuit)
determine how deep the UF must be buried?
I
didn't see that detail in the code book.

Size and kind of cable:The chart I looked at says I would have to use a
#1 copper, or a 2/0 aluminum cable for the application.
I used the middle column, 75 celcius. Is this corret?
If so, I'm assuming aluminum is cheaper. Is there an underground
feeder that is aluminum? If so, what kind of wire is
it? USE, etc? Which would you use?


So, my 2 questions are:
1) How deep?
2) What kind and size of cable?
 
  #11  
Old 03-19-06, 07:46 AM
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Originally Posted by Willg54
I'm feeding
Size and kind of cable:The chart I looked at says I would have to use a
#1 copper, or a 2/0 aluminum cable for the application.
I used the middle column, 75 celcius. Is this corret?
If so, I'm assuming aluminum is cheaper. Is there an underground
feeder that is aluminum? If so, what kind of wire is
it? USE, etc? Which would you use?
If you have your heart set on direct burial, I would not use direct burial aluminum. If you get one pin prick in the insulation jacket you’re going to see failure of the wire very quickly. You’re talking 50', I would run sch 40 underground, pvc is not that expensive in the whole scheme of things, you’re talking about adding maybe another $50-$100 onto the project. Just think you'll never have to dig up your yard again if that cable fails and you can run all the aluminum you want. Then again what I did at my place is run 1 1/4 pvc sch 40 with #2 copper thwn, with #8 copper ground, to my 100A sub panel in my garage. By the time you added the cost of each individual conductor together and the PVC I was at the same price of buying direct burial aluminum wire, and I do not have aluminum I have good old copper. Although your prices may not be anywhere near what I get them for I get a slight discount so you would have to price it out. Get quotes for the wire and pvc from your local supply house. You might be surprised and see that the big home stores are more expensive for pvc and wire.

-Roy
 
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