I have always used emt for feeders unless they go underground or are in wet/corrosive environments. I have seen rigid pvc used in multistory apartments to feed subpanels. There is no real AHJ outside of the city here except for co-op people and I would like to know the legality of this along with the benefits or drawbacks. Are there problems with smoke or flame spread that might be covered by other codes? It was 90 deg. C. pvc. used with thhn. I noticed they had a pull box every two ninety's, to keep from melting them, I beleive.