# designing conduit run for underground fibre installation into a building.



## cdnelectrician (Mar 14, 2008)

Depends on the type and size of cable they put in but it should be fine, when it comes to fiber they always over size the conduits by quite a bit. If you have room, use 15 degree bends instead of 22.5 bends.


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## farlsincharge (Dec 31, 2010)

it says 24 sme, and it is about the size of a 1/0 rw90 copper conductor


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## MDShunk (Jan 7, 2007)

You can actually increase the sidewall pressure using the more shallow bends. That can be the death of fiber sometimes. There's some free online sidewall pressure calculators. The manufacturer of the cable normally has installation details also. I think Polywater's was the best software, but I heard some time back that it's no longer free. 

TRICK: I've pre-installed the fiber in straight 3/4" black well pump tubing on the ground, and pulled that tubing through the conduit, eliminating any pull on the fiber.


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## sxpert (Jun 17, 2011)

your best bet, if it's allowable by code, would be to use HDPE conduit. the important thing here is the curve radius, should be about 2 to 3 feet


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## farlsincharge (Dec 31, 2010)

I think it may be a moot point anyhow. The cable has been coiled outside on the ground for over a year with no end cap on it. It comes out of the ground in a piece of 2 inch duct at which point it is bent over in a hard 90 to lay on the ground. I mean a hard 90, like it could be in a 2 inch LB.

Amateur hour.


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## mikeh32 (Feb 16, 2009)

Let me see if i can find my fiber install guide thing. Its at my other house, so I will pm you 2morrow


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## Pliersonfire (Jun 22, 2011)

Wait! You running met underground? How about PVC?new fiber doesn't the long sweeps it used to.


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## Pliersonfire (Jun 22, 2011)

I mean emt


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## cdnelectrician (Mar 14, 2008)

If it's outdoor fiber your pulling in I wouldn't worry TOO much, the new cable they are making is pretty tough, especially outdoor cable. 2 inch is fine as long as you don't have too many bends and they aren't tight.


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## mikeh32 (Feb 16, 2009)

cdnelectrician said:


> If it's outdoor fiber your pulling in I wouldn't worry TOO much, the new cable they are making is pretty tough, especially outdoor cable. 2 inch is fine as long as you don't have too many bends and they aren't tight.


even the new outdoor cable sucks....

If it was so great, they wouldnt be replacing all the traffic runs with radio


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## MisterCMK (Jul 5, 2009)

MDShunk said:


> You can actually increase the sidewall pressure using the more shallow bends. That can be the death of fiber sometimes. There's some free online sidewall pressure calculators. The manufacturer of the cable normally has installation details also. I think Polywater's was the best software, but I heard some time back that it's no longer free.
> 
> TRICK: I've pre-installed the fiber in straight 3/4" black well pump tubing on the ground, and pulled that tubing through the conduit, eliminating any pull on the fiber.





cdnelectrician said:


> If it's outdoor fiber your pulling in I wouldn't worry TOO much, the new cable they are making is pretty tough, especially outdoor cable. 2 inch is fine as long as you don't have too many bends and they aren't tight.


You would have to get pretty nuts to actually damage a burial fiber. Fiber is a lot stronger in regards to installation that people give it credit for. That is a good thing though.



mikeh32 said:


> even the new outdoor cable sucks....
> 
> If it was so great, they wouldnt be replacing all the traffic runs with radio


What traffic runs are you talking about?


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## chewy (May 9, 2010)

The most likely problem your going to face is the corners being to tight, I prefer to just man haul external work and leave the tugger on the truck as its quicker and we had one man hole to man hole under a road and something went tits up with the under road boring and poking the conduit through, we tried to manhaul it but it was only giving about half a metre before my legs turned to jelly so we set the tugger up and snapped a couple of strands of that rope so had to kill it, we ended up having to add a connection onto the run for both the fibre and copper. 

On this particular job we had our cables run over by dump trucks, apparently road cones dont apply to roadworkers, we also had a concrete truck sideswipe a drum of cable sitting in the yard by our office and dent the fibre cable quite noticebly not to mention completely trashing the drum, we also over handeled it alot because of the layout of the pits and limited by the gear we had so we had to man haul for each 200m run between pits then figure 8, flip it and start the process again, even after all that we got 72 little red lights show up on the FOBOT so happy days. 

The last certification I was at they had some direct buried fibre that had an armoured outer, and a high tensile steel core that you needed special parrot cutters for, you couldnt bend it by hand past its bend radius.


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## don_resqcapt19 (Jul 18, 2010)

How far are you running in the building? It is my opinion that 770.48 limits you to 50' of unlisted fiber in the building. Most underground fiber is not listed. Some will say that there is no limit when the fiber is in one of the raceways listed in 770.48(B), but I don't agree. The limit is set in 770.48(A) and (B) just tells you that it has to be in a raceway without increasing the pemited distance.


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