how many urd in a ditch

[khill327]

how many sets of urd's can install in one ditch ??? I have see a ditch with 20 pairs of wires . could this be ok

 

[augie47]

It appears to me that the wording of 310.15(B)(2) and 310.16 covers direct buried cables, so at your 4th conductor, derating would apply.
In the same manner, the ambient correction factors may help you,

side note: True URD (with no associated RHW, USE, XHHW rating) is not a reconginzed NEC wirng method.