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I am installing a media enclosure in an under-stairway closet on my first floor. I plan on running Schedule 40 PVC conduit between the enclosure and the crawlspace directly below, as well as between the enclosure and the attic, via a penetration between floors. These conduits will all carry low voltage data cables, and one fiber cable from the crawl space. I plan on using fire rated foam to seal all of the annular space around the floor and ceiling penetrations.

I want to make sure I stay on the right side of the NEC, and would appreciate some help in interpreting the requirements I need to meet.

Article 800 covers data and network cable.

800.110 Raceways, Cable Routing Assemblies, and Cable Trays says...

Wires and cables shall be ... installed in raceways that comply with either...

  • Raceways Recognized in Chapter 3.

  • Communications Raceways.

I prefer the Chapter 3 option, which then 352.30 further says:

PVC Conduit shall be installed as a complete system as provided in 300.18...

300.18 says...

Raceways, other than busways or exposed raceways... ... shall be installed complete between outlet, junction, or splicing points prior to the installation of conductors.

It however goes further to say...

Exception: Short sections of raceways used to contain conductors or cable assemblies for protection from physical damage shall not be required to be installed complete between outlet, junction, or splicing points.

So, here are some of my questions:

  1. What would be considered a "Short" section of raceway? The vertical raceway going from my cabinet into the crawlspace is less than 3 feet at the moment. Does this count as short enough that I wouldn't need a "complete system"?
  2. If a complete system isn't necessary, can I just have the PVC Conduit sit flush with the wood in the crawlspace, or should the conduit extend a certain number of inches into the unfinished space before I cut it?
  3. If a complete system is necessary, is it enough for me to add just a box at the end of my PVC run in the crawlspace, leaving the actual box open so that fiber, coax, or ethernet cables can be fed into the conduit from the box?
  4. Is it okay to support this conduit with PVC hangers/straps if the penetration isn't close enough to a joist to secure it directly?
  5. Is there anything else I'm not thinking of that would fail me in an inspection?
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    do you even need conduit for low voltage wiring? I thought it was only for mains and DC> 40v...
    – dandavis
    Oct 17, 2023 at 19:31
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    the AHJ is who should be answering these questions. but really, you're getting a residential low voltage inspection? why bother? the real answer to all your questions is "it doesn't matter" and "nobody cares; do it however you want, just don't damage the wires"
    – ickybus
    Oct 17, 2023 at 19:32
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    @dandavis I don't need conduit, i am doing it for ease of access for running wires in the future, as well as protecting the exposed fiber line that will be run from the Demarc outside to the media cabinet through the crawlspace. Oct 17, 2023 at 19:32
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    About the only thing an inspector/NEC might mention concerning low voltage wiring is if it looks neat. Conduit looks neat but you could use an old garden hose or not for what NEC cares. NEC deals with plus 50 voltage, household electrical(120v/240v).
    – crip659
    Oct 17, 2023 at 19:34
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    Fair enough, it's a decent question with a great answer; "it don't matter".
    – dandavis
    Oct 17, 2023 at 19:35

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While it's unlikely that your LAHJ will specifically inspect your LV cabling, it's prudent to follow code regardless. Code is, at its root, about saving lives, mostly from fires, (the body that pubishes NEC (or NFPA 70) being the National Fire Prevention Association.) In the case of LV cabling that's mostly about using correctly rated cables that don't make too much poisonous smoke (smoke being what kills most people who die in fires.)

The short section of conduit language is primarily about protecting cables that otherwise don't need conduit where they need protecting. It's subject to interpretation (in the event that an inspection even happens) but it's not uncommon to have 20 feet of conduit running up a wall that just bends out and ends where wiring will be strung along roof trusses 20 feet up so the length of the "short section" is not subject to a hard limit. A reasonable person might wonder about 10 feet of conduit for 12 feet of cable, though, depending on details.

You can end the conduit at the floor or below the floor, or you can consider how much you'd like to bet on never, ever, having rodents make it into your house and decide to run the conduits complete; one reason being to keep the cables from being nibbled on (yes, that happens) and another reason (which may or may not apply in your case) is to make running more cables easier if you'd have to crawl to an awkward spot to get cables into your short conduit, where you could just pull them through if you assembled conduit through that awkward spot, once.

You should at minimum ease the sharp inside edge of the conduit where it ends, or preferably use a bell-end fitting to protect the cables as the enter and leave the conduit if they are not coming in via a box. That is a fitting with a rounded shape,

conduit bell end

Image source https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.mainelectricsupply.com%2Fecomm_images%2Fitems%2Fmedium%2Fpvcb300.jpg&f=1&nofb=1&ipt=dd0c55ead2474c3168ebc3e066bf5dd9e715103db653373589b04f37e6b47dd2&ipo=images no endorsement implied

not the "bell-end" of a conduit that is designed to glue to another conduit without needing a coupling, by having its end enlarged.

bell-ended conduits

Image source https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fstatic.grainger.com%2Frp%2Fs%2Fis%2Fimage%2FGrainger%2F4ETY5_AS01%3F%24mdmain%24&f=1&nofb=1&ipt=17c9d98bbe5deaae2c844fe2b572877b49ab0cb13290f0a610f86e0671524e0a&ipo=images no endorsment implied

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  • Thank you for sharing your input. While I agree it's unlikely to trip me up with an inspector, article 800 is part of NEC so I'll consider this best answer Oct 17, 2023 at 23:31

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