Depth of Cover

[hyattjay]

Is there a hard and fast maximum depth of cover for direct burial feeders (transformer to distribution panel)? Our team is looking at the options including OH and UG, with and without conduit/raceway.

 

[LarryFine]

Look at NEC Table 310.5

 

[ron]

I think Larry mean 300.5 for the minimum cover requirements for <1000V.

Maximum depth is not established, except if the feeder is critical, I would suggest doing Neher McGrath calculations, as the deeper you get, the more of a derate on the conductor ampacity gets, due to difficulty in emitting heat to the environment.

 

[LarryFine]

I think Larry mean 300.5 for the minimum cover requirements for <1000V.

Oops!

 

[hyattjay]

Thanks. We opted to direct bury the cable at 36".

 

[Little Bill]

Thanks. We opted to direct bury the cable at 36".

The 36" is measured from the top of the cable or raceway.

 

[hyattjay]

Correct, the Depth of Cover will be 36" from top of the cable to top of finished grade. Cable will be on 3" of fine sands, covered by 6" of fine sands, then back filled to top of finished grade, a red warning tape is installed 12" above the cable (If I recall the detail from the contractor correctly).

 

[infinity]

Correct, the Depth of Cover will be 36" from top of the cable to top of finished grade. Cable will be on 3" of fine sands, covered by 6" of fine sands, then back filled to top of finished grade, a red warning tape is installed 12" above the cable (If I recall the detail from the contractor correctly).

I don't think that you can do better than that for direct burial.