Cross-post from IP
Would like to start a dialog about Code and performance requirements for cables installed in floor boxes or conduits encased in concrete. These are typically conference rooms with mics, data, HDMI, etc but are becoming more and more common as people finish basements, garages etc. This thread deals ONLY with concrete in direct contact with the ground(slab).

I ran into this a few weeks ago and thought I might be able to save some headache for someone else.
The install was an older building wired years ago by another LV company. Swapped a mixer and had noise from three mics that had cables running through conduit into floor boxes. Investigated and found water in the conduits. Electrician said ‘wet location, use the right cables’. Dug in and found the following:

From the NEC definition:
Location, Wet. Installations underground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.

By definition, this conduit and any boxes/conduits that any of us install in slabs are considered to be in a wet location.

NEC 300.5
(B) Wet Locations
The interior of enclosures or raceways installed underground shall be considered to be a wet location. Insulated conductors and cables installed in these enclosures or raceways in underground installations shall be listed for use in wet locations and shall comply with 310.10(C). Any connections or splices in an underground installation shall be approved for wet locations.
Also NEC 300.9 Raceways in Wet Locations Above
grade
. Where raceways are installed in wet locations above grade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations
above grade shall comply with 310.10(C).

NEC 310.10 (c) Wet Locations
Insulated conductors and cables used in wet locations shall comply with one of the following:
(1) Be moisture-impervious metal-sheathed.
(2) Be types MTW, RHW, RHW-2, TW, THW, THW-2, THHN, THWN, THWN-2, XHHW, XHHW-2, ZW
(3) Be of a type listed for use in wet locations.

Where this leads us is to the conclusion that any cables that we install in wet locations need to be rated for wet location use. This is where the discussion splits into legal versus operational.

Legal – Is this a correct interpretation of this rule? There are a lot of exclusions granted for communication cables, but none seem to trump the general location/rating issue. Most of the installation references in 700-800 point to Chapter 3 raceways.
There are some exclusions still on the books for POTS, but where does this leave Data, HDMI, VGA, Audio, HDBase-T, etc? What does the 2017 say? It appears that the reason this hasn’t been a big issue is that in a lot of cases, the low-voltage cables get installed in the conduits after final inspection has been completed and therefore the conduits get inspected, but not the cables that end up inside them.

Operational – Even if you can legally find an exclusion that allows you to get away with using a cable not rated for the application, is this doing your clients a big disservice? It is a fact of life that conduits and boxes in slabs will eventually have water in them. Cables sitting in water will fail eventually. Should we opt to take the high road on this issue and always install ‘wet-location rated’ cables any time that we run into a slab? Who is a good supplier for wet-location rated HDMI cables?