Bend Radius–The unseen problem!

Bend Radius – The unseen problem!

How much can we bend a fibre optic cable without kinking, twisting, damaging or shortening the fibre optic cables life in any way?

Bend Radius

Let’s start with Wikipedia’s definition of Bend Radius –

Bend radius, which is measured to the inside curvature, is the minimum radius one can bend a pipe, tube, sheet, cable or hose while not kinking it, damaging it, or shortening its life. The smaller the bend radius, the larger the material flexibility (as the radius of curvature decreases, the curvature increases).

However, the fibre optic industry mainly refers to the bend radius of a fibre optic cable as ten times the outer diameter after installation.

So using an example: - if you have a 2mm standard jacketed fibre optic cable then you should not have any bends less than 20mm in diameter.

You also need to take note that the bend radius will vary depending on the fibre optic cable type being installed. In other word’s the cable design has a lot to do with it as well.

We generally use two terms when it comes to bend radius:-

- Short-term bend radius – This is the maximum bend whilst installing. It is the larger of the two bend radii.

- Long-term bend radius – This is the tightest recommended bend after installation and is the smaller of the two.

Impact of bending on the fibre.

The biggest problem is that you can’t really see bend radius issues during the installation. And it does have an impact on the long-term reliability of the signal and the attenuation or loss of signal.

So, what can you do to prevent it?

Here are some thing to consider:-

- Make sure you always handle to cable properly!

- Try to avoid any reverse bending or twisting when taking the cable off the drum.

-Always unwind in a figure 8 configuration, this also allows for easy pulling of the fibre optic cable in both directions.

-When securing a fibre optic cable to another cable or patch panel, etc. make sure you don’t tighten the zip-tie, velcro, or whatever else you might be using your using too much causing stress on the fibre.

- Keep the cable from being routed off sharp angled edges.

A Current Solution in the marketplace.

Reduced bend radius fibre is a huge innovation for optical networks because it allows more flexibility in bending fibre around tight corners without any discernible increase in attenuation. These fibre’s are often referred to as "bend insensitive," or "bend resistant" -- terms that can be somewhat misleading when it comes to the actual capabilities of the fibre.

The figure below shows the difference between standard cable and bend insensitive cable at the time of publication. No doubt there will be more improvements to come in the future.

Fibre Optic World

Bend insensitive fibre is less sensitive but not in-sensitive. So a word of warning, still take care of your cable regardless. We will discuss bend-insensitive fibre in one of our upcoming issues, so stay tuned!

Conclusion :-

Never exceed the cable bend radius!

Fibre optic cable can be broken when kinked, twisted or bent too tightly around corners, especially during pulling. This can cause real issues to any network.

A fibre optic cable should not be installed with a bend radius smaller than twenty (20) times the cable diameter. After installation, the fibre optic cable should not have any bend radius smaller than ten (10) times the cable diameter.

If fibre optic cable is handled with the correct consideration you can prevent most issues caused by exceeding the bend radius of the cable installed!

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