FIBER RUNS

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Alwayslearningelec

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Is there usually more or less waste when it comes to electricians pulling/running fiber as opposed to THHN etc. and why? I would imagine there would be a lot less due to cost. THanks !!!!!
 
What kind of waste?

If you mean excess cable after the pull, probably the fiber runs would result in longer scraps to be sure that the length ordered was sufficient. Less waste that way, in the big picture.
 
Volta said:
What kind of waste?

If you mean excess cable after the pull, probably the fiber runs would result in longer scraps to be sure that the length ordered was sufficient. Less waste that way, in the big picture.
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Thanks Volta. Yes, excess cable aftert the pull. What do you mean longer scraps but less waste? THanks again.
 
Just that if the length ordered would happen to be too short, there would be a great waste of time, labor, and the fiber. It is unlikely that an unexpected splice would be accepted in fiber, but THHN would rarely be much of a problem.
 
When designing fiber runs I and everyone else I know add a foot or two to each of the measurements then add 2% cut lenght at the end. I do this because you can't just splice fiber anywhere and running short and having to reorder your fiber will get you in major trouble so better to have too much than too little.
 
Jhaney said:
When designing fiber runs I and everyone else I know add a foot or two to each of the measurements then add 2% cut lenght at the end. I do this because you can't just splice fiber anywhere and running short and having to reorder your fiber will get you in major trouble so better to have too much than too little.
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Why can't you splice fiber just anywhere? Where can it be spliced? IF you had a 2,000' run how much "extra" would you add...in your opinion? Thanks,.
 
Every splice and connection as well as bends that are too tight add to the dB loss in the fiber. Too much loss and it won't work. Most of the time the specs will tell if and where the fiber is to be spliced.
 
don_resqcapt19 said:
Every splice and connection as well as bends that are too tight add to the dB loss in the fiber. Too much loss and it won't work. Most of the time the specs will tell if and where the fiber is to be spliced.
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What about a fusion splice? Those barely add any significant db loss (if executed correctly).
 
MAK said:
What about a fusion splice? Those barely add any significant db loss (if executed correctly).
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They still add some and very often the number and location of splices is covered by the design documents. Some of the mechanical splices have loss that are very close to those of a fusion splice.
 
horsegoer said:
Is there usually more or less waste when it comes to electricians pulling/running fiber as opposed to THHN etc. and why? I would imagine there would be a lot less due to cost. THanks !!!!!
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When ordering fiber I get the actual length of the run estimated as close as possible, add double the length of the termination room for each end, and then add 10%. I will NEVER get to the end and not have enough. An FOA certified installer will tell you that this IS the way to estimate your length, because at the termination points, you can very easily run out of slack, which would never be acceptable.

In addition, as a termination practice, any slack (waste as you seemed to imply) will be coiled very loosely, but in a neat, and workmanlike manner in spaces provided for that purpose just above or inside the actual termination point. Fiber cables are not cut "exactly to length."

Also, a comment about splicing: if the splice is not specified in the drawings, and an installer just added one somewhere, even with the appropriate protections in place, the cable would be reordered and pulled again without the splice on the jobs I've worked.
 
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horsegoer said:
Why can't you splice fiber just anywhere? Where can it be spliced? IF you had a 2,000' run how much "extra" would you add...in your opinion? Thanks,.
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For a typical 2000' run:

1. 2,000 foot run (assuming [always a bad thing] accurate measures: 2,000'
2. Termination at one end: 40' x 40' termination room with floor access to the cabinets: 120'
3. Termination at other end: field cabinet: 20'
4. Add 10% 220'

Total: 2,350'

As to the assumption in #1, I do what Jhaney mentioned to get the original length figures, always measuring several times, and ordering once. ;)

This is actually how we do it.

In the termination room, when I'm done, the cable will enter at one point, neatly make its way under the floor to the opposite side of the room, and then go at right angles with appropriate bends to the cabinet it needs to arrive at, where another 30 feet will be coiled at that point and then it will enter the cabinet. Hope this helps you understand the process.
 
Also check the specs to see if they require extra cable as "service loops". I worked a under ground run of about 2.5 (one splice) miles that required 4 complete loops around the inside of a 10' square manhole at each end of the run and 2 loops around the center manhole where the cable was spliced.
 
Assuming you have a 2000 foot run of multimode fiber with no splices, just point to point, how much fiber would you leave at each end at the points of termination? Would it change if it were single mode?
 
don_resqcapt19 said:
Also check the specs to see if they require extra cable as "service loops". I worked a under ground run of about 2.5 (one splice) miles that required 4 complete loops around the inside of a 10' square manhole at each end of the run and 2 loops around the center manhole where the cable was spliced.
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So is this how the phone company/cable TV guys have enough wire to reach their truck/trailer

where they do their work ?
 
John120/240 said:
So is this how the phone company/cable TV guys have enough wire to reach their truck/trailer

where they do their work ?
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Yes, such service loops are always required for fusion splices which are commonly used by the utilities. My job used mechanical splices, but still required the service loops, but we made our connections in place without needing the service loops.
 
horsegoer said:
Is there usually more or less waste when it comes to electricians pulling/running fiber as opposed to THHN etc. and why? I would imagine there would be a lot less due to cost. THanks !!!!!
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Depends on if the electricians are familiar with working with fiber or not.

We had electricians destroy about 150' of a fiber pull because they did not tie to the kevlar when they started pulling as well as appropriately feed the pull.

Same site, we had a different EC leave 40' of fiber coiled up within a handhold on a pole that fed a camera...all within a 6" square at most pole. They wasted that whole pull and we had to fight to get slack just so we could reterminate and then run jumpers to feed the cameras.

I've seen some good electricians with fiber and some terrible. We have a joke about some of them....how their loss and attenuation is so high, but they can't understand, they used the good blue/orange wire nuts on their ends.
 
MAK said:
Assuming you have a 2000 foot run of multimode fiber with no splices, just point to point, how much fiber would you leave at each end at the points of termination? Would it change if it were single mode?
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How much you leave coiled up depends on how close you can get the fiber splice trailer to the site and whether the fiber is buried (in a hand hole), in a manhole or up on a pole. Max loop is 100' but at any dead end location on a pole line there is a minimum of 30' maintenance loop placed just in case that pole needs to be changed out.
 
horsegoer said:
Why can't you splice fiber just anywhere? Where can it be spliced? IF you had a 2,000' run how much "extra" would you add...in your opinion? Thanks,.
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You can't just place a splice anywhere because the DB loss added by each splice no matter if your using a fusion splicer or mechanical splice each extra DB addes just a little more loss to the circuit and limits the type of speed you can provide. Also all splice locations need to have accessibility with slack built in to splice it properly.
Hope this helps
 
Jhaney said:
How much you leave coiled up depends on how close you can get the fiber splice trailer to the site and whether the fiber is buried (in a hand hole), in a manhole or up on a pole. Max loop is 100' but at any dead end location on a pole line there is a minimum of 30' maintenance loop placed just in case that pole needs to be changed out.
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What limits the service loop to a maximum of 100'?
 
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