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I have done some searching around but have not found anything definitive, and/or my background is weak in this area and I may be understanding poorly.

I will have 2-4 PoE cables that will be run underground a distance of up to 300ft. There will be no sources of interference near the cables. There will most likely be 4 cables, with the possibility of others in the future.

My guess was that I would want a 2" conduit to run these through. I have seen it suggested that PVC be used for this, which I assume refers to some flexible PVC conduit, which I have not found in 2" x 300ft variety, if I remember correctly, or it is too expensive.

I have also seen Carlon's Carflex Liquidtight conduit (https://carlonsales.com/carflexliquidtightnmconduitparts.php), but these appear to be expensive for my basic needs and the 2" conduit Edit Meant to say that the 2" conduit only goes up to 100'

Currently, it appears that the cheapest solution would be to run each cable in its own 3/4"-1" PEX tubing, but I would rather leave room for further cable(s) in the future, and a separate conduit for each cable is awkward. I understand that direct burial with appropriately shielded cable is also an option but I would rather allow, again, for addition of cables, but also cable replacement, without unearthing the trench.

I wonder if anyone has any recommendations for materials or specific products.

edit devices are going to be PoE cameras

  • I take it that trenching as deep as you need to is a non-issue? Also, I take it you are getting outdoor (direct burial/weatherproof) rated Ethernet cable for this as well? – ThreePhaseEel Jul 6 at 20:07
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    The issue is underground ducts have a nasty tendency of ending up damp or even flooded, so even if you don't need mechanical protection (because that is provided by the duct) you do need a higher level of waterproofing than typical indoor insulation provides. – Peter Green Jul 6 at 23:50
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    @petergreen the best way to mitigate the risk of water ingress into underground conduit is fill it with water. Now there's no question :) Also, it will help it stay put during the backfill... seriously Code assumes buried conduit is 100% full of water 100% of the time. .. – Harper Jul 7 at 0:27
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    If the plan is to add more cables at a later date wouldn't it be more useful install a fibre-optic cable instead of Ethernet cables as you're also bordering on the maximum Ethernet cable length at 300'? Then you can place a PoE switch at you're location to supply whatever networking needs you have there. – yetanothercoder Jul 7 at 11:41
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    You can improve the question by adding SI units. You can write other units in brackets. – Jonas Stein Jul 7 at 12:13
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Speaking as someone who does a LOT of data cables...

Pray to your deity of choice regarding (lack of) lightning nearby. The extent to which I prefer fiber optic for outside data runs is influenced by years of dealing with copper outside data runs, and the failures resulting - but few, if any, cameras are set up for power + fiber optic, so you'll want a nice POE-friendly surge suppressor at the point where these cables enter your building, tied into the building grounding/earthing system. Else you will have burnt out data ports, almost certainly, eventually.

As already mentioned, don't even think of putting non-wet-rated cable in exterior conduit. It may work for a while, but it will fail, usually at "not a good time." I personally prefer a "dry gel" cable and tend to get stuff which purports to be direct burial, but I run it in conduit as I hate digging trenches twice, and I trust rodents to chew on direct burial cables.

You can not bother to glue the joints at all, or you can glue the joints with great care. If the conduit is PERFECTLY waterproof, it will still fill with water, as moist air will enter and moisture will condense, and stay in the conduit. All outside conduits are defined as wet locations, and all cables in them must be wet rated, or failures will be expected.

Run 2" conduit if you like, but it's going to be massive overkill for four 4-pair data cables unless you get some absurdly thick jackets. Nice to have more room than you need, but there is a point of absurdity. Two examples of 24AWG Cat 5e direct burial in stock are right around 0.25" diameter for a net area of 0.05 square inches each - roughly equivalent to 6AWG wire, where (less than) 40% fill would be 1" (rigid) schedule 80 conduit, (or 3/4" schedule 40, but I prefer 80 by a large margin.) So 1-1/4" would be more than generous sizing and cost you quite a bit less. Where things are more unknown, 2" is nice just because if you don't know, you don't, but if 4 data cables is it, 2" is, IMHO, Massive Overkill. Save your money for something you actually need... Like those POE surge suppressors (not cheap, but inexpensive as compared to the equipment you will lose otherwise.)

Most "real" POE devices work just fine at 100 meters on 24Ga cable from the 48V POE power supply - the device power supply is generally flexible and expects to be able to work on a short cable at full voltage or a long cable at lower delivered voltage, and most are not power hogs anyway. Early "half-baked" POE systems varied a lot more wildly, as may things which ARE powerhogs and outside the "real" POE standards.

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    And he won't want just any old surge suppressor either, he'll want something that's UL497 approved as a primary protector if he's in an area with any significant lightning exposure – ThreePhaseEel Jul 7 at 0:56
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    "PERFECTLY waterproof" stuff is also great at holding water in. – Criggie Jul 7 at 7:17
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    If you're gonna run fiber optic, then run mains power. Because mains and fiber can share a conduit. Throw a couple #12 THWN's in there and put 240V on em. Now even at 20A breaker trip limit you'll have a bearable 7% drop... and for your local PoE power supply, switch and a couple of LED security lights, not even 1% drop. Add a portable step down transformer and you even have 120V for tools. – Harper Jul 7 at 12:01
  • Thanks for this answer @Ecnerwal. – user98368 Jul 8 at 0:00
  • @Harper I was actually planning on running fiber as well, but to a location further on (500ft). As for these #12 THWN cables, I did not realize it was that easy or even feasible to run this much power this distance. How should I go about calculating what I can do with this cable? In this case, I understand that these cameras will be able to do with the PoE cables alone, but there will be other power needs elsewhere, including up to 1500-2000ft away. There I was just going to use solar. – user98368 Jul 8 at 0:02
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The upside of data cables is there's no limit to how many you can run in one conduit -- no 310.15(b)(3) thermal current limits (PoE may change that), and no 225.30(D) limits on multiple circuits. Really, your problem is all about the ease of pulling multiple cables this long distance, especially given the delicacy of Ethernet. Larger diameter conduit and fewer bends helps a lot with this.

If your notion is that PoE has no distance limit, you will want to very, very, carefully research the particular power needs of your devices, and revisit that assumption.

When we talk about "PVC conduit" we mean 10 foot sticks. You don't buy it in reels. The problem with reels (far as NEC is concerned) is that the stuff has to be fairly flexible to go on a reel, and if it's flexible, it's going to lay down with lots of bends. Those bends, added together, will exceed the 360 degrees allowed between pulling points. This rule is entirely about practicality of pulling, so it applies to you.

Liquidtight is a lost cause. You don't keep water out of conduit by NASA-tier conduit sealing and gluing and anti-condensation humidity control forever. You presume it is 100% filled with water 100% of the time, and use cable rated for that.

I would go one of two ways.

Two conduits

One for data cables, and the other for the inevitable mains power. (Low-voltage is out of the question at these long distances). Given my fondness for stepping up mains AC for long distances, I would probably use 1" for the mains power and 2" for all data (for easy pulling without rending the cables).

The big downside of this is that you have to be serious about conduit cover for the mains wiring... PVC would need to have at least 18" of dirt over top of it (so a 21" trench).

Rather Fat low voltage wire

Go all-in with low voltage <30V, and just use some really fat wire to endure the voltage drop. If you're contemplating #8 copper or larger, it's time to switch to aluminum wire. In this case you'd have all powered devices draw from the same pair of wires. Which would be fused at the source for appropriate thermal limits. It could also be DC, which removes the issue of crosstalk between power and data (not that that's much of an issue).

Then, because it is low voltage, you get to put it in the same conduit as ethernet.

  • Thanks. I should have clarified the devices. They are PoE cameras and I do believe that they will be OK at that distance without dedicated power, with a 48V injector at the other end. I believe they are under 20W. For example they might be around 12V 1A. I was just going to use some ordinary Cat 5e or Cat 6 cable for each device. Is this incorrect? I was hoping to avoid gluing all the PVC segments together, and I feel like it is prone to leaking, but maybe that means I should be getting cable that is rated for that. – user98368 Jul 6 at 23:18
  • Well, 24AWG cat 5 wire is 2.5 ohms per 100', so 15 ohms in your case. Do the math or bench test it with a 15 ohm power resistor. I wouldn't glue the middle sections either, leave a bit of room for expansion like 1/8". Mind you code says glue 'em. I would glue near the ends. – Harper Jul 7 at 0:00
  • Ah, I see now that it would not be necessary to glue for this application. No codes in this area actually. OK, I will do the research on this power issue. – user98368 Jul 7 at 0:09
  • @user98368 At that distance, you definitely want to run the largest-gauge Ethernet you can get, usually 23AWG, and you'll probably be needing gel-filled. – chrylis Jul 7 at 19:40
  • @chrylis Since the devices each are only something like: 12V 1A, do I need to worry about gauge? My understanding is that the voltage loss will be the issue with distance and that this will be fine in this case due to the low voltage. I haven't had a chance to double check any of this though. – user98368 Jul 8 at 0:15

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