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Originally asked at Network Engineering

What types of communication cables can pass through electrical conduit?

I believe that optical fiber is the only one possible. However, I'm not sure.

I'm trying to make a home project where I have wifi APs interconnected by some wire. The type of wire can vary, but I'd prefer to have the lowest priced tech. Also, would prefer to have all wires hidden, so this is why I'm considering to use electrical conduit.

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    Do you mean running in the SAME conduit as electric wiring? – longneck Apr 22 at 15:13
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    Yes, it would run both the electrical wiring and the communications one. Are there viable combinations? – ruasoliveira Apr 22 at 15:17
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    Are you just trying to use existing conduit, or is the line voltage wiring in the conduit only for the APs power? If so, why not get APs that support PoE (Power over Ethernet), which allows them to be powered by the ethernet cable. – PhilippNagel Apr 22 at 15:23
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    PoE is a great option for a lot of APs. With or without PoE, keep in mind that Ethernet cabling can be fished pretty much anywhere - i.e., it can be hidden inside walls without using conduit. – manassehkatz-Reinstate Monica Apr 22 at 15:41
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    What is the voltage rating of your communications cable? They can be run together if proper voltage com cable is used but not usually recommended because of noise on the power side causing problems. – Ed Beal Apr 22 at 15:58
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You just can't do it. There are only two exceptions where you can intermix comms and mains voltage in a conduit.

  • Fiber-optic cable, where the cable is entirely non-conductive, is acceptable with mains
  • SCADA controls where the interlink is related to the mains equipment, or to be more precise, where all of the low-voltage wiring remains entirely contained within Class I wiring methods, e.g. power-rated conduit, and that means not coming out to a socket and continuing onward with non-mains-rated cable, i.e. ethernet is Right Out. Examples:
    • 3-way retrofit smart switches, where the switches re-task the existing mains /3+ground cable to be always-hot, neutral, and a comms wire.
    • Powerline monitoring and load-usage devices such as Sense, EnergyCurb, etc. These live entirely inside the service panel, and their signal lines (current transformers) are wired entirely inside mains wiring methods. This is a great example of how there isn't any Ethernet port on the side of your service panel (huge no-no!!), instead WiFi is used, which provides the mandatory isolation. Essentially this whole data network "lives at live voltage" and is contained thusly.
    • Commercial RR7 lighting installations, where 24VAC signals throw relays to operate lighting.
    • Industrial SCADA, where the controllers sit on mains power, and the interconnect is via an Ethernet/Canbus/whatever thrown into the mains conduit or raceway, and the equipment is designed to accommodate this method. If the SCADA equipment has an Ethernet port to the "outside world", that port is built isolated and is UL-listed to that effect.

I am assuming you are dealing with equipment that takes a lot of power, like a server rack. If you are only hauling AC power in that conduit to feed a "wall wart" power supply that's low voltage and <55W, then forget AC -- haul the low voltage. An obvious method is PoE (Power Over Ethernet). However you can do this with any low-voltage load, just carefully mind your voltage drop and feel free to dip into the mains electrical parts bin for the fat wires you may need. For instance, if you need #10 wire, then use readily available, cheap, stranded white THHN, and use it for both low-voltage + and -. (tape the ends of the wires red and black to designate polarity etc. You are allowed to re-tape individual wires to different purposes in conduit when it's low-voltage wiring.)

If you just can't haul low voltage, yet your load is <40W, the other super sneaky way to haul low voltage while still having mains at both ends, is use two 40W thermostat transformers back-to-back, so the transmission through the low-voltage conduit happens at 24VAC.

  • Not true, if the com wire has the voltage rating for the mains wiring it can be run in the same conduit or wireway, – Ed Beal Apr 24 at 14:53
  • @edbeal that goes without saying but that is not enough. You can't just toss an ethenet into a mains conduit and bring it out to a wallplate in a 2-gang right next to a power plug, then run a common ethernet cable to your PC. That is what everyone wants to do, of course. – Harper - Reinstate Monica Apr 24 at 15:30
  • With a devider or separation you can do that with a 2 gang , don't forget the devider adds to the box fill, I have done this many times , once the inspector verify it is legal they have signed off on cover inspections in both my current county and the last 2 I used to work. – Ed Beal Apr 24 at 16:22
  • Wait, are you saying ethernet and THHN are in the same pipe!??? coz the whole point of a divider is... – Harper - Reinstate Monica Apr 24 at 16:23
  • @Harper -- with the divider, they enter via two different pipes I bet. (There are circumstances where you can use an innerduct to separate comms from THHN inside an outder conduit, but normal branch circuit conduits are too small for that trick) – ThreePhaseEel Apr 24 at 22:40
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If you are "considering conduit" and you actually need line voltage and low voltage, "consider" TWO conduits, one for low voltage/communications wiring and one for line voltage.

If all you need is to power access points, use POE and Cat5e or Cat 6a (either is fine for gigabit. 6a buys you some hope of 10 gig if you actually have hopes for that, but conduit means you can run the cheapest wire (5e) now and replace it if or when you exceed what it can do, easily. Which is the BEST reason to use conduit for network wiring.) Ignore Cat6 wothout the a, it's a waste of your time and money.

"Power line interference" is mostly a myth. Twisted pair communications cable is specifically designed to reject outside interference by its construction and the way signals are encoded/decoded. 50/60 Hz "noise" won't impact it at all. You'd have to have some incredible high frequency noise feeding into the power lines to have any effect on it. I know this because I do it for a living, and I have LOTS of network cables that make long runs near power cables due to crappy old buildings where there's no choice other than that, and I have switches that report error rates - which are pretty much always nil unless there's physical damage to a cable. Dang rodents - another reason to use conduit if you can.

I love fiber, but using fiber "inside your house to access points" will be prohibitively expensive (at the present time - in 10 years, you may be happy you have run conduit.) All my access points are connected by wires. Fibers (at present, for home-scale and even campus-scale use) are for between buildings, or a few special cases that are unlikely in a house.

As Harper mentions, "fiber optic" is not enough - it has to be a fully dielectric (non-conductive) cable construction , which is easy enough to come by, but there are fiber optic cables that have a conductive element (such as a tracer wire, or POE wires), and those are NOT acceptable in line voltage conduits. A line voltage conduit (with line voltage wires) is also what a fiber installer would consider a very hostile environment for a fiber cable, which is not happy about various forms of abuse such as sharp bends.

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CAT6 is repetitively cheap and can be run through conduit. Depending on the diameter of the conduit and the amount of cabling you may not be able to use pre-terminated ends and will require you to terminate the ends. If you are running it for APs in the house then I wouldn't worry about conduit. You can fish cabling through walls although two story homes can cause some issues with placement and you may want to use a low-voltage contractor.

  • No, you are missing a subtext here: he wants to share conduit between mains wiring and comms wiring, which is a rather big no-no (see NEC 800.133) – ThreePhaseEel Apr 24 at 22:39

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