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?

It usually comes down to cost. What is your client willing to spend?

HDMI for wet locations, I would recommend direct burial Cat cable with extenders. If the customer says cost is too high, then give them what they want and have them sign a waiver that the cable is not rated for this enviorment.

How does water get in the conduit? Unglued or poorly glued junctions? Does the glue eventually fail? Is the glue permeable? Is the conduit permeable? I always assumed schedule 80 with properly glued junctions were water tight. Wrong?

We do not deal with this often so I am just throwing curiosity out there.

Condensation...

Difference in temperature of the air in the conduit and the outside/inside wall of the conduit.

Oh duh. Must be late. :p

See 800.47. The requirements that insulated conductors and cables in wet locations be listed for wet locations [310.10(C) do not apply to communications cables.

All of the cable types mentioned in article 310 are for power and light.

The way the NEC is written, the first 3 chapters set the groundwork for installation of any kind of cable or device, but anything specific to low voltage starts in chapter 8. (That is oversimplified but close enough)

Is it a good idea? Yes. Always practical, especially with preterminated HDMI? No

You do a huge disservice to your customer not using OSP cable in "wet locations" and buried conduit always becomes a wet location. Odds are you will not find any HDMI cable that will suffice. OSP rated Cat cables/fiber and extenders is the best option.

800.47 deals with underground cables entering into a building, 800.110 is for cables inside buildings.
800 Section V - Installation Methods Within Buildings
800.110 Raceways for Communication Wires and Cables
800.110(A) Types of Raceways
Communication wires and cables shall be permitted to be installed in any raceway that complies with either (A)(1) or (A)(2).
(1) Raceways recognized in Chapter 3
Communications wires and cables shall be permitted to be installed in any raceway included in Chapter 3. The raceways shall be installed in accordance with the requirements of Chapter 3.
(2) Other permitted raceways
Communications wires and cables shall be permitted to be installed in listed Plenum communication raceway, listed riser communication raceway, or listed general purpose communication raceway selected in accordance with the provisions of 800.113 and installed in accordance with 362.24 through 362.56, where the requirements applicable to electrical non-metallic tubing apply.
800.113 (A) Listing
Communication wires, cables, and raceways installed in buildings shall be listed.

I do not see anywhere other than 800.47 any exceptions that would allow for cables not 'wet-location' rated to be installed in conduit in a slab inside of a building. Quite the opposite as 800.113 (A) requires all communication cables installed inside of a building to be listed.

We live in what is considered a 'desert' due to limited annual rainfall. In this last case, this was the amount of water that could be vacuumed out of a 1" conduit no more than 30' in length before it went up a wall.
[Link: photos.app.goo.gl]

As you can see, any cable that sits in this for a period of time will fail and they will look like this:
[Link: photos.app.goo.gl]


Edited to fix photos

Somewhat true, but 800.47 explicitly says "underground communications wires" not only "cables entering buildings." It's not only what they say, but sometimes what they don't.


800.113(A) simply requires that they be listed. If it's a plenum, use plenum wire. If it's riser, use riser wire. 800.110 also indicates that communications wire *CAN* be installed into designated raceways. Not that they have to.

There are only so many listings for Communications wire. Plenum, Riser, General Purpose. There is no provision for underground like other wire types. OSP or Outside Plant is a good idea but not required by any means.

I only know all this because a few years ago I did 432 classroom hours of training on the NEC and other NFPA publications for an Oregon Limited Energy A license.

I will have to agree to disagree. 800.110 fits better when dealing explicitly with cables inside of a building. In order for 800.47 to apply, the slab would have to be classified as 'underground' and not inside the building. If the slab is considered inside the building, then the exemption from 800.47 would not apply and the installation methods in chapter 3 would govern our conduits.


I did my OR LE years ago and while the classes teach a lot, there is always more to learn and not even the AHJ knows it all.

i see no images or links but when i reply it appears something is attached to your post.

PVC is not water permeable.
Schedule 10 is used for sprinklers all the time.
Schedule 80 is simply thicker, offering additional protections against damage.

Jason, your pics are not showing up on my computer.
Did you host them on Pakistani porn server that my host is blocking?

If by Pakistani porn server, you mean Google photos, then yes. Yes I did host them there.....
Forgot that google photos always works for the owner of the photos, and others cannot view.