What Article states you can not put NM cable in PVC. Article 336-6 says you must protect NM cable from damage and one of the means is schedule 80 PVC. Article 347 on PVC has no mention of not using it to protect NM cable. I know of Article 400-8(6) that says you cannot run cord in a raceway (except as otherwise permitted in the code, but it provides no hint of where that is.)
