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We have AIS fiber and I was wondering how tight I can make the radii when re-routing the cable? 
 

I understand the old rule-of-thumb is ten-times the OD, but not sure if that is still current.

 

 

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Ours has at least one 90o bend with no apparent issues.

Edit:  That's a curved 90, not a right angle.

Edited by bankruatsteve
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21 minutes ago, Crossy said:

 

Yeah, ours is similar.

 

Fibre is amazingly resiliant when in its jacket, but don't take any risks with it, you can't twist it back together.

 

https://www.essentracomponents.com/en-us/news/product-resources/fiber-optics-faqs-the-advantages-bend-radius-explained-and-more

 

My rabbit chewed through my 3BB cable, tried cutting and butt joining, didn't work.

Had to get 3BB out to replace it, with involved a machine in a suitcase, which seemed to heat and melt.

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Just found this thread. Does anybody know if the joins the True installer put in, in the picture below, would have any impact on the efficacy of the fibre?

Unfortunately he ran the cable and was going to leave a big loose arc until I "asked" him to tidy it up as with the previous co ax. I thought he would have to have rerun it from the box across the street but no........

 

IMG_20201104_115622.thumb.jpg.b1971a1e42881bb313867ab581ce04b9.jpg

 

 

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6 minutes ago, topt said:

Just found this thread. Does anybody know if the joins the True installer put in, in the picture below, would have any impact on the efficacy of the fibre?

 

Unless your signal to noise ratio is already marginal a well made joint shouldn't have any noticeable effect.

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9 minutes ago, topt said:

Just found this thread. Does anybody know if the joins the True installer put in, in the picture below, would have any impact on the efficacy of the fibre?

Unfortunately he ran the cable and was going to leave a big loose arc until I "asked" him to tidy it up as with the previous co ax. I thought he would have to have rerun it from the box across the street but no........

 

IMG_20201104_115622.thumb.jpg.b1971a1e42881bb313867ab581ce04b9.jpg

 

 

As long as you get the speed you pay for everything is okay. The cable might not be perfect but still good enough. 

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  • 3 weeks later...

Contrary to popular assumptions, single mode fibre optic cores are so thin and flexible they can be tied in knots without breaking as long as it's kept in it's jacketing. There is also little detectable difference in attenuation if a 20 km fibre run is coiled up on it's drum, or pulled out straight. As for the above picture, I would personally criticise the installer for leaving the connections vulnerable to dust and grime penetration.

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On 10/27/2020 at 3:21 PM, BritManToo said:

Had to get 3BB out to replace it, with involved a machine in a suitcase, which seemed to heat and melt.

Yes "fusion splicing".

I think that's what they do. Requires a trained technician.

Just butting together will yield bad results (signal loss) and probably not work.

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The 10X OD minimum bend radius rule can be misleading. It depends on the cables construction. The minimum for a bare single fibre would be about 50mm, although if it was to be coiled I would increase it to 100mm. For a large fibre count cable with internal tubes can be as much as 1 meter, more if it is armoured.

 

The bend radius in Sometimewoodworkers picture is fine (although I would have flipped the black cable so the termination end exited on the left, and had less of a bend into the termination box).

 

The bend radius in Mogandave’s post is too sharp. If the cable is a internal pigtail type ( like the yellow cable in sometimewoodworker’s post), you probably will not damage the cable, but may get what is called pressure points. For domestic use you will probably not notice, but for a commercial use it would not be acceptable. I would have run it in the ceiling then done the wall, negating the need for sharp bends.

 

The reason for minimum bend radius for a single fibre is as follows. The fibre itself is very flexible and can bend much smaller the the minimum radius (although there is a limit and will eventually break if too small), but will result is degradation of the signal. If you see a single fibre what you see is an coloured 250 micron fibre. If you strip the outer coloured protective layer you are left with a 125 micron glass fibre. Within this fibre is a 9 micron inner glass central core. The inner core is slightly more pure than the outer core and has a different refractive index. (Ever see a spoon standing in a glass of water and seems to bend where it enters the water? Same principle) The signal light is sent down the inner 9 micron inner core. It stays in the inner core due the bouncing off the outer core because of the different refractive index. If the fibre is bent too far the different index cannot over come the bend and light will escape resulting in loss of signal. This is commonly known as a pressure point.

 

Topt, your picture is of 2 pre terminated single fibre cables joined via a through connector (they just click together). They are not designed for external use. You may or may not have problems in the future. The installer was just lazy to run the correct length cable.

 

As too why different cables have different minimum bend radius is a whole new subject.

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