I'm looking at applications regarding conduit that will be beneath a slab. I understand that sheathed wire is not approved by code for inside conduit that is buried. I'm sure there's a reason why, but I'd sure like to understand this reason.

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Originally Posted by HockeyFan

I understand that sheathed wire is not approved by code for inside conduit that is buried. I'm sure there's a reason why, but I'd sure like to understand this reason.

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This is certainly not true. While it is poor practice to use cable in conduit, it is not expressly forbidden.

You need to use W (wet) rated conductors in an underground conduit. Most THHN today is dual rated THHN/THWN.

One reason I like Conduit and individual wires is if wiring gets damaged, it can be replaced and you won't be screwed. If wiring was going to an island or adding a wire for switchleg, anything, It can save you/ anyone Money down the road. I don't even like romex in the walls, for the fact it is usually obsolete the moment it is installed. Things usually have to be destroyed for future needs.