I may have to run 1200 feet of fiberotptic cable and AC power cable. I would run PVC conduit in a trench with the fiber inside. I can buy pre-terminated non-conductive outdoor fiberoptic cables in this length range. But has anyone ever done such a long pull? I don't think it is advisable to break the fiber into shorter segments due to return loss, etc. I only need two strands of fiber, but I will probably buy cable with more strands just in case there is some need in the future. Six strands seems to be common.

Ideally I would like to run the fiber in the same conduit as the power, but this seems perplexing.

In order to manage pulling the copper wire, I think I will need to break it up into 300 foot runs with intermediate pull boxes. It seems like it would be extra work to pull the fiber through the segments 300 feet at a time. Also, some segments would experience extra friction. Basically, whatever is going into a conduit segment should be pulled all at once in one go, it seems to me. But this will be hard if the copper is in 300 foot segments and the fiber is one continuous run.

I could run the fiber through its own conduit, but if I don't need to do that, I don't want to. I mean, I am paying for the conduit. Also, seems like it would be a difficult pull. (Please comment if you have experience).

Anyway, if you have done something like this, please let me know what the best way to do it is.

I am adding this information because I think people will ask. The copper wire will be 240V (two hots no neutral). I will run AWG14 THHN wire. There is not much of a load up there, and the load can tolerate a very wide voltage range (down to 100V). Ampacity is fine and I can live with the voltage drop. Will also run a 14AWG ground wire. Will install ground electrodes at far end.

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    Have you done a voltage drop calculation on it, or are you just guessing? This is one place you really want to get the voltage calc correct. FYi, THWN-2 wire comes in 500' lengths, so a splice every 240' or 490‘ may be a better choice than 300', Commented Nov 7, 2018 at 6:54
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    Good call on the lengths. Yeah. I went through calculations. 14 AWG is 2.52 Ohms per 1000 feet. So for 2400 feet (round trip distance) it is 2.4 * 2.52 = 6 Ohms. Peak load is around 300 Watts. So in that condition the current will be around 1.3A. So the drop will be around 7.8V. That gives power at load of 1.3A * (240V - 7.8V) = 302W. Load is a battery charger that functions down to 100V. Average load will be much less than 300W (more like 10W).
    – mkeith
    Commented Nov 7, 2018 at 8:15

1 Answer 1


I think in this case, I'd go with a direct burial armored fiber optic cable in the same trench, rather than running it in the conduit with the power. Here is my reasoning.

The all dielectric cable you can run in the same conduit with the power is not rodent resistant. I would be concerned about rodent damage in your pulling points. I think an armored fiber buried in the same trench will be safer.

It will be much, much easier to install - almost foolproof. No pulling the delicate preterminated ends through the conduit. Put the spool on a pipe and have two people walk it down the trench and it will be laid about as fast as you can walk 1200 feet.

The only problem is if the direct burial fiber ever gets damaged, it will be very expensive to locate and repair the fault; but realistically, in that event, you can just install an all dielectric fiber in the power conduit and abandon the damaged cable in the ground.

That is one reason to oversize the conduit a bit. Don't try to go real close to the conduit fill limit. That's a terrible way to save a few bucks. Other reasons to oversize the conduit - easier pulling and leaves you with the option to install bigger wire later, just in case.

Consider using the big sweeps for your 90° bends. Large diameter pre-made PVC 90's are readily available.

I'd try to keep the 90°'s to a minimum - go for straight pulls from handhole to handhole. The telecom standards want you to avoid making bends in boxes, they recommend a straight through pull. I think that guideline (it's not a code requirement) makes sense for workstation runs in EMT in buildings, I don't think it makes sense with a long underground run like this.

For the power - its probably not worth worrying about in this case, but don't rule out aluminum. Aluminum is lighter, so it creates less friction in the pipe and pulls easier. It might save money. Since you'll probably be terminating in disconnects at both ends, terminating is not an issue. Your splices in the handholes will be easier with copper, since wet location wire nuts are readily available.

In the comments, @Harper recommends limiting the distance between pulling points to 240' or 490' to stay closer to what's on a spool of wire. I'd go a little closer if possible - say 220' - because the longest fish tape I have is 240'. At least it was 240' when it was new, it has lost a few feet. This may or may not ever matter, just another thing to weigh in your planning.

I always include a pull string when I pull wire. With PVC, I do not use inexpensive polypropylene string for pull strings, it is too likely to burn through a 90. I use mule tape, which is flat nylon, or scrap wire or cable. It's mainly there as a last resort - I'd rather use a fish tape - but it's easy enough to pull one in and better to have it and not need it than need it and not have it.

The three most important things when pulling wire: LUBE, LUBE, LUBE. Maybe you like the yellow waxy stuff (it freezes in the winter) maybe you like the blue goo like I do, maybe you prefer the new less-mess clear stuff, but whatever you do, lube. Lube more than you think you need. Way more.

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