Pull Box Size For Fiber

[sparkky302]

Do I need to size a pull box on the exterior of the building that is for fiber optic cable per 314? What I have is a 4" conduit coming out of the ground and entering a pull box on the exterior of the building. From there we are downsizing the conduit to 2" inside the building. Do I need a 24x24 can because of the 4" conduit? Can I use an 4" LB?
Thank You

 

[fmtjfw]

Pull boxes for fiber are usually much larger than for wire. It has do with safe bending radiuses and space to handle the fiber. I think LB are a serious no-no. That's the story we got from the Telephone Company when we ran conduit for a 24 pair fiber cables (about 1 inch in diameter (weather rated cable). The other trick is to place the boxes in the straight part of the runs and make all bends using long sweeps rather than standard factory 90s.


Just one person's experience.

 

[don_resqcapt19]

You have to look at the minimun bending radius of the fiber cable. Sometimes that requires larger enclosures than does the rules in 314.28.

 

[tom baker]

And there is a difference between the bending radius under tension and the relaxed radius. We use 30x30x24 in ground concrete handholes.

 

[Jhaney]

the bending radius of fiber is 10 times the diameter of the cable when not under load and 20 times the diameter of the cable when under load. generally the minimum pull box size is 12"L x 12"W x 6"D.

 

[don_resqcapt19]

the bending radius of fiber is 10 times the diameter of the cable when not under load and 20 times the diameter of the cable when under load. generally the minimum pull box size is 12"L x 12"W x 6"D.

The bending radius is specified by the cable manufacturer. They are not all the same. You need to look at the information for the actual cable that is to be installed.

 

[Jhaney]

The cable bending radius is the same no matter who we get it from because the bending radius is dependent on the failure or leakage of light from the fiber. some cable will bend tighter but will loose its ability to accurately transmitt the data due to leakage. Now if we were talking about regular copper cable I would agree with you but Fiber is a completely different animal.

 

[don_resqcapt19]

The cable bending radius is the same no matter who we get it from because the bending radius is dependent on the failure or leakage of light from the fiber. some cable will bend tighter but will loose its ability to accurately transmitt the data due to leakage. Now if we were talking about regular copper cable I would agree with you but Fiber is a completely different animal.

At least on manufacturer has a fiber on the market that has a much tighter bend radius than standard fiber. It addition the bending radius of the fiber cable is also based on the make up of the cable itself and not just the glass. The very first outside fiber that I installed had a 5/16" center fiber glass strength member and that cable had a very large minimum bending radius ... much larger than what would be required for the prevention of light leakage.

I wish I would have kept a 5 or 600' length to use a "fish" tape. We pushed it in 4" underground 4 to 500' and it worked better than any fish tape I ever used.