If the concern is a fire starting then I gather it has to be completely surrounded by very fire resistant material. So for example a racking system that just encloses conductors between the rack and the flammable back-film of the module isn't really sufficient. I think maybe the reason that PVC wasn't specified is that it can actually burst into flame, unlike metal under atmospheric conditions. Of course if the PVC is underground then the flames aren't likely to get so far.
Originally Posted by Carultch