Underground Wire & Conduit Code requirement?

[l3city]

Hi fellas, recently a plan required that all underground wire be minimium #10, in 3/4" PVC 40 conduit unless noted otherwise. Is it required by the NEC or is just the engineer's design?
thanks ahead for any input fellas!!
:smile:

 

[Jljohnson]

Engineer design. NEC does not stipulate.

 

[infinity]

Could be a voltage drop issue. Certainly not an NEC issue. I would think that specing THWN would be more important than #10 conductors but someone had a specific reason for this.