Underground DC conduit depth

[electro7]

I was wondering if I could get some help on depth for DC conduit 600V max.

We were unable to get to 18" of cover on some PV Source Circuits with maximum voltage of 600V in PVC Sch. 40 conduit..

In 300.5 would I be looking at Column 3 at a minimum cover of 12" with 2" of concrete on top of conduits?

 

[masterinbama]

Concrete

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[jaggedben]

You could ask this in the main NEC forum. Nothing special about PV conductors when it comes to cover requirements.