Topic: Fiber Optic Cable Bend Radius
Table of Contents: The FOA Reference Guide To Fiber Optics

Fiber Optic Cable Bend Radius

All fiber optic cables have specifications that must not be exceeded during installation to prevent irreparable damage to the cable. This includes pulling tension, minimum bend radius and crush loads. Installers must understand these specifications and know how to pull cables without damaging them.

Not following bend radius guidelines can lead to cable damage. If the cable is damaged in installation, the manufacturer's warranty is voided. Here is what one manufacturer's warranty says: "This warranty does not apply to normal wear and tear or damage caused by negligence, lack of maintenance, accident, abnormal operation, improper installation or service, unauthorized repair, fire, floods, and acts of God."

Bend radius
Bending of a fiber optic cable can damage the cable if the radius of the bend is too small. Damage may include broken fibers, fibers with higher loss due to stress and cable structural damage that may lead to reliability problems.

The normal recommendation for fiber optic cable bend radius is the minimum bend radius under tension during pulling is 20 times the diameter of the cable. When not under tension (after installation), the minimum recommended long term bend radius is 10 times the cable diameter.

Fiber Optic Cable Bend Radius

Under tension (top) and after installation (bottom)

Note: Always check the cable specifications for cables you are installing as some cables such as the high fiber count cables have different bend radius specifications from regular cables!

Bend radius example: A cable 13mm (0.5") diameter would have a minimum bend radius under tension of 20 X 13mm = 260mm (20 x 0.5" = 10") That means if you are pulling this cable over a pulley, that pulley should have a minimum radius of 260mm/10" or a diameter of 520mm/20" - don't get radius and diameter mixed up!

bend radius
Example of cable bend radius violations - the pulley on the truck used to turn the cable toward the capstan pulling it is 5-6 times too small for the cable - the red dotted circle shows the proper diameter - and the cable is being pulled out of the conduit up out of the manhole at an extreme angle, exceeding the cable bend radius where it exits the conduit.

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Table of Contents: The FOA Reference Guide To Fiber Optics


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