NM buried in plastic conduit

[Homeownerinburb]

A friend wants to energize his new Jacuzzi, 50 amp 240v.

I am thinking of running 8-3 nm under the house then going directly into plastic conduit for the section that needs to go underground. The nm is marked for interior use, am I violating code by running it in conduit underground?

 

[hj]

1. moisture could still get into the conduit
2. The wires will run hotter if they are enclosed in the conduit.
3. EITHER reason would be enough to not do it.