Fiber Optic Cable

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Dennis Alwon

Dennis Alwon

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Does anyone have any info on how far fiber optic can be safely pulled. I am told 300 lbs of force is the maximum but how do you figure that out? The pull is 600' with only 1" conduit but I am thinking we will need a few pull boxes.

Any help?
 
A good basic overview of pulling fiber:
http://www.thefoa.org/tech/ref/install/installcbl.html

I would check with the cable manufacturer - each cable will have different ratings for pulling force. I've seen some types that have a max pulling tension of just 10 lbs. !

Important to note is that FO cable is VERY sensitive to bending. Depending on the cable type, what you might consider a minor bend may actually cause damage to the fiber.
 
zbang said:
Really depends on the cable itself- some has strength members and some will stretch like warm taffy. Only 300 pounds sounds like pretty lightweight stuff. Hate to say it, but you'll need to ask the manufacturer.
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That is what I told the guy that is involved in this. They want me to run the conduit and figure out where the pulls would be needed. I said he better ask the manufacturer as I am not taking that responsibility.

BTW, it is a very small cable for a gate.
 
bward said:
A good basic overview of pulling fiber:
http://www.thefoa.org/tech/ref/install/installcbl.html

I would check with the cable manufacturer - each cable will have different ratings for pulling force. I've seen some types that have a max pulling tension of just 10 lbs. !

Important to note is that FO cable is VERY sensitive to bending. Depending on the cable type, what you might consider a minor bend may actually cause damage to the fiber.
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Do you think a standard electric 90 in pvc may be too sharp?
 
Dennis Alwon said:
Do you think a standard electric 90 in pvc may be too sharp?
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This may help:

If no specific recommendations are available from the cable manufacturer, the cable should not be pulled over a bend radius smaller than twenty (20) times the cable diameter. After completion of the pull, the cable should not have any bend radius smaller than ten (10) times the cable diameter.
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If I was installing that, I would only be using pull boxes where I needed them to avoid exceeding 360? degrees of bend. You want to limit the pull points as much as you can...every time you handle the fiber, you have another chance of damaging it.

You would have to check the minimum bend radius for the fiber, but it would be unlikely that a standard 1" elbow would be too tight of a radius.

You could try a pulling calculation using this calculator.
I would run it using an single aluminum conductor with about the same OD as the fiber. If this shows less than 300 pounds of tension, you would be good to go. The actual pulling tension for the fiber would be less because the fiber will weigh less than the aluminum you used in the calculation.
 
Thanks all. I appreciate the feedback. I probably will not be doing the pulling but I may be installing the conduit and I want to make sure there are no issues. The contractor is calling the manufacturer also just to be safe.
 
Dennis Alwon said:
Thanks all. I appreciate the feedback. I probably will not be doing the pulling but I may be installing the conduit and I want to make sure there are no issues. The contractor is calling the manufacturer also just to be safe.
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If the conduit has not yet been laid, I'd use long sweep elbows versus standard 90's. Might also be worth considering going up a size on the conduit.
 
Once I installed 150' of 1" smurf conduit (per AT&Tspec), then had very hard time pulling the fiber.

If you, can do 2" or larger conduit with sweeps and 24" pull box in the center.

If the conduit or the turns are too tight the fiber will break.
 
This run is exterior to a gate. I think 600 feet without a box will work from what I have gathered from 2 forums but I may add a pull box.
 
Jon456 said:
I'd use long sweep elbows versus standard 90's. Might also be worth considering going up a size on the conduit.
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+1 for this.

You might also be able to find direct-burial rated cable, or armored cable and simply be able to attach it directly to the wall, no conduit or pulling needed - not sure what the specifics of your install are.

Also, who will be terminating the fiber? I would recommend you not use pre-terminated fiber, as pulling with connectors preinstalled is just asking for trouble.

Also also, how many fibers do you need for the application? The cost difference for a 4 fiber cable vs a 2 fiber cable is probably minimal. You might want to do this to have some spares in case there's any damage or future upgrade required. Recently did a job where the original design called for 6 fibers in one location, but I ran a 12-fiber cable as that's what I bought for another part of the job. 2 days after the pull, we needed to use 8 of the 12 to connect some other equipment that was "forgotten" in the spec.
 
I see no reason to use long radius elbows for this installation. I also see no reason to increase the conduit size, assuming that the fiber is below the maximum wire fill.
 
The installer got back to me today and would prefer long radius bends-- of course but he also wants 3 hand holes just because....????

So I guess we will install a hand hole every 150' and make him happy--- I guess he is thinking for future stuff-- I don't care if that is what they want I will do it-- I'll get paid so.....

Thanks again-- I tend to think we could get by without any hand holes and standard bends from what I've seen. He insists 1" conduit is fine
 
Dennis Alwon said:
The installer got back to me today and would prefer long radius bends-- of course but he also wants 3 hand holes just because....????

So I guess we will install a hand hole every 150' and make him happy--- I guess he is thinking for future stuff-- I don't care if that is what they want I will do it-- I'll get paid so.....

Thanks again-- I tend to think we could get by without any hand holes and standard bends from what I've seen. He insists 1" conduit is fine
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As long as he will be pulling and take responsibility for the fiber then 1" is what he gets.
 
Sometimes the max length is based on the fishing tape, or rods. Our PUD fiber guys like 500 ft which to me seems short, perhaps 1,000 feet with2" conduit and long sweeps.
 
don_resqcapt19 said:
This is a small diameter cable. You don't gain anything by installing an oversized conduit.
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The cable that I had trouble with was small, 2 or 4 fiber cable, but with the kevlar and the outer jacket it was about 3/8" across.
 
tom baker said:
Sometimes the max length is based on the fishing tape, or rods. Our PUD fiber guys like 500 ft which to me seems short, perhaps 1,000 feet with2" conduit and long sweeps.
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That was his argument for wanting pull boxes at 150'. His fish tape is only 200 feet so he feels that it would be beneficial for others as well. I don't buy it but we will put the boxes in as he asked.
 
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