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Old 08-03-2013, 11:04 AM   #1
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Direct Bury conductors to detached garage sub-panel


We were doing some yard work recently and discovered that a previous owner of our house direct buried (3) #2 AL conductors about 3 inches deep along a run of about 35 feet across the yard to the garage panel. What's extra scary is that the conductors run along the back of a flower garden area where digging regularly happens. We also noticed that an additional #6 copper THWN conductor was run about an inch deep about a foot away from the other cables. We proceeded to dig up the cables so that we can relocate and bury at the proper depth (breaker is of course shut off in main panel). Can someone confirm the required direct bury depth for the conductors? I've read 18" some places and 24" in others. I guess to be safe I could just go 24". Also, can all of the wires go into the same trench, or does the ground need to be run separately? Fortunately we're re-routing the conductors so we should have plenty of extra length to be able to bury them deeper. Finally, looking at the panel it appears that the grounds and neutrals are all connected and there isn't a separate ground rod for the garage. Should I drive a ground rod outside of the garage and run an additional ground from the sub-panel to the ground rod? Your advice is appreciated.

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Old 08-03-2013, 12:09 PM   #2
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Direct Bury conductors to detached garage sub-panel


If these are individual conductors, you can't just bury them, they need to be in conduit, with at least 18" of dirt over the top.

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Old 08-03-2013, 12:17 PM   #3
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Direct Bury conductors to detached garage sub-panel


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Originally Posted by Old College Try View Post
I've read 18" some places and 24" in others. I guess to be safe I could just go 24".
From the '08 code, table 300.5, 24" from grade to the top of the conductors. So about a 27" trench. 18" to top of conductors is for beneath 2" of concrete(a sidewalk) or running PVC pipe.
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Also, can all of the wires go into the same trench, or does the ground need to be run separately?
Same trench.
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Originally Posted by Old College Try View Post
Should I drive a ground rod outside of the garage and run an additional ground from the sub-panel to the ground rod?
Two ground rods, #8 copper and protected with PVC pipe where exposed.

Seperate the grounds and neutrals in the subpanel.
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Old 08-03-2013, 12:47 PM   #4
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Direct Bury conductors to detached garage sub-panel


If there is not a ground rod their may be a connection to a ufer instead. Suggest to check this before going to the effort of installing ground rods. The wires have to be direct burial rated (typically at 24"), or wet rated and placed in conduit (typically at 18").

I recommend over-sized conduit and 18". You can readily replace with larger wires if ever needed in the future, and less digging.
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Old 08-03-2013, 01:04 PM   #5
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Direct Bury conductors to detached garage sub-panel


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If these are individual conductors, you can't just bury them...
If Direct Burial is printed on the insulation, it seems you can. Chapter 3, 310.7

Wires must be protected from physical damage, where exposed, and to a depth of 18". Easiest is to sleeve them in schedule 80.
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