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I'm looking at running some OM3 fiber (outdoor, armored), 6 strand between two residential buildings (think from a house to a garage for example). It's about 150ft total.

I do not want to run copper (ground loop concerns, grounding in general, lightning/surge protection).

The fiber cable has a minimum bend radius (unloaded) of about 11.5cm (4.5 in).

I had been planning direct bury the cable (it's rated for it), then in to conduit as it exits the ground and in to a conduit body to enter/exit the buildings. But seeing the required minimum radius I don't think I'll be anywhere near the proper bend radius with any of the LBs I've looked at.

(I am considering using conduit for the full run as well, but that's here nor there right now).

For now the main thing I'm concerned with is how best to get the cable in/out of the building while maintaining the required minimum bend radius?

Jonathan
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  1. For your stub from underground, use large-diameter sweeps instead of standard 90 degree bends. For ease of pulling think at least double your min. bend radius.

  2. When entering the building, run the sweep parallel to the wall rather than perpendicular. To enter the bottom of the sweep from the trench, make a big wide horizontal bend.

  3. At the top of your sweep where you intend to penetrate the wall, use an LB, but use a big one (we use 4" on jobs I've done, but we're pulling 24 strand minimum. You could probably get away with 1-1/2" or 2". I always figure conduit is cheaper than wire so don't be afraid to oversize. I believe the Verizon fiber coming into my house underground is in 1" PVC but they price it by the truckload.)

  4. When you get inside, run your fiber onto your backboard or into your pull box vertically, so that if you are looking at a cutaway cross section of your wall, you'll have a mainly vertical run from the ground, through your LB, and up the interior side, with the fiber running almost vertical.

You want the cable to be only slightly offset as it goes through the LB and into whatever indoor enclosure you will use. Think of a racing driver cutting two opposite corners with a single sweeping line.

ThisOneGoesToEleven
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Don't do OM3 today. Run single mode. The fiber is cheaper as it's more commonly deployed, it supports higher speeds and longer reaches, and the optics is almost at the same price.

In addition, remember that the bend radius given in data sheets is the bend radius where the cable will retain the rating. You probably have a short run, so a 3dB loss in the cable is probably not a disaster: your link budget allows for this.

In short: for such a deployment I'd be comfortable with going down to 1/4 of the bend radius given in datasheets, and accepting the increased loss.

As pointed out by ecnerwal, it's also possible to get reduced bend radius fiber. It's slightly more expensive, but allows for tighter installation runs.

vidarlo
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