atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring Running fiber-optic cable in existing pipes.

Anybody know the limits of common fiber-optic cable? I am wanting to pull through an existing PVC conduit run in between buildings. The run is approximately 55 foot in lenght, 1.25 inch PVC pipe. It has a plated LB at each end with a standard 90 about 36 inches below the LB at each end. I don't know if fiber will pull through 4 PVC 90's and survive. Thanks for the info in advance, everyones experience in here helps me out and even saves my butt a lot of times!

Pull the cable gently and relax the turn in the LB and you will be fine. Leave the bend of the cable inside the LB's loose just to keep it graceful. Today's fiber cable is a lot more resilient than it used to be.

You will be fine in 1-1/4 pipe as long as you aren't using OSP fiber cable. Use the indoor-outdoor cable which handles just like indoor cable with small diameters but does the underground thing fine.

What Ed said,.............fiber is a lot stronger than anyone thinks.

I have pulled the crap out of indoor grade fiber......to the point where I just knew it would be damaged, but it wasn't.

I agree with Ed and Mike. I've pulled a lot of fiber thru even smaller conduit than that with 3 to 4 90's.

You also should consider a jug of lube, and libe the hel@ out of it.

Kirk

Ok, to tack on a question to this topic. I recently went out to terminate fiber pulled in by another tech. It was the indoor/outdoor stuff. The fiber had been pulled so hard that the fiber was all rippled. Needless to say, it didn't pass. I attempted to pull in another 6-strand (original was also 6-strand). The conduit is 1-1/4", just over 500 feet, with either 3 90's, or 2 90's and a 45. They pulled in a 12-pair OSP when they pulled in the first 6-strand. I used that 6-strand to pull in the second. I got 150 feet into the conduit, and could go any further. At that point, the jacket was stretching so badly that when letting go of the cable, about 5 feet would immediately shrink back into the pipe. If I gave it more time, probably another 5 feet would shrink into the pipe.

So my question is, what is the length limit between pull boxes? This run went from a building, to a pull box about 25 feet from that building, and then all the way to the box inside the other building (over 500 feet from pull box to inside box). The customer is having their electrician come back in and install at least 1 pull box in the middle of the run.

Okay, it's 4 a.m. and I'm writing a book. If you need clarification, PM me and I'll try to help.

This goes to the NEC --- and the number of 90s (no more than four between pull boxes). I did a lot of paper mills, pull boxes every 100 ft. and it still is hard to pull. Even with lube. The heat makes the sheath "drag" and stick, the lube dries out and has to be wet down.

Number One Suggestion --- Don't pull on the sheath -- that causes "piggy tails" in the fiber, that twisting funny looking over-twist. Strip out about 1 -2 foot of sheath. Take the Kevlar, twist it into a "rope", cut out the glass, set your swivel, and pull with even, measured strokes. The Kevlar will act as a pulling snoot/sleeve.

Number TWO Suggestion --- Use a gel type fiber lube. It dries so the termination is easy without a gooey mess. Add water and it is slick as snot again. I'll tell a funny story about that sometime in the "Booth".

Now you know why OSP telephone conduit is always 4". You stated they pulled in an OSP 12 and this six ---- they are wrapped around each other (BETCHA !) and after pulling the 125' it has tightened around the OSP and knotted. You will need to pull out both the 12 and old 6 pulling in a pull rope as you go. Put your new six in with the old 12, use a swivel, pull away, re-terminate the 12 and terminate the 6. As the cable is pulled back in, have a helper "feed" it in spread as far as possible so it doesn't twist. With the swivel and a leader this should not allow much if any wrapping of the two cables around each other.
Fiber manufactureres have different specs on pulling (just as copper does) but you can put more stress on fiber if done correctly than you are allowed on Cat 5. They also sell "break-aways" set to break during pulling so you don't over-stress the fiber. I have cheated and just use swivels for fishing lines --- catfish can get big! Just remember to put a slack loop between the pull rope and the cable around the swivel in case it breaks.

Yeah, it ain't easy, but if it were anyone could do it.


Other OSP tricks work good with fiber, just have to use some imaginative techniques.

KLD

I agree totally with KLD on those pulling methods and he's right, that 12 in there was the problem. You would have to pull it out and start from scratch with everything at that kind of distance.

He mentioned the break-away, great idea and a cheap idea in comparison to screwing 500 ft of new fiber. For that distance, we would have used a tugger. The good tuggers have a clutch you can set with the maximum allowable tension from your fiber specs.

Can you get an interduct in it?

Interduct thru an 1-1/4" conduit? I don't think there would be any chance of getting that in. What's the motive behind your question, just out of curiosity?

We have had similar situations where the GC puts in conduits that are way too small. They seem to forget that you can yank the crap out of electrical wire, but not so with telephone cable or fiber. The smallest we have ever had to deal with was 1.5". In this instance, we used 3/4" black poly water pipe as our "inner duct" for the fiber along with the 50 pair copper. It was still a struggle over a 350 foot run, but at least the fiber went through unharmed. We used a conduit blower to shoot a pull string through the water pipe.

They won't ever learn though. Gone are the days of two 4" conduits like the telcos demanded (and got) from the GC. It's not the GC's fault though, it is the architects who mandate the construction standards.