Going to clean up NM cable hanging down all over the place under mobil home. 550,15H states must be in conduit approved for use where subject to physical damage. Really??? How would it be damaged under a home? Actually, it says approved for wet location OR subject to physical damage, so technically just need one or the other. I'm thinking sch40 pvc or ENT. Should be correct, right? Also, can someone tell me about RTRC? Just happen to see it in the code book today, never heard of it