You have been asked to project manage a fiber cable backbone installation. In the course of the installation, you notice the fiber cable with a 25 mm (1 in) outside diameter is being installed into…

ANSI/TIA-568 and BICSI standards specify that the long-term minimum bend radius for fiber optic cable after installation is completed equals 10 times the cable outside diameter. Applying this multiplier to a 25 mm (1 in) OD cable yields 250 mm, which the standard rounds to 254 mm (10 in). Bending fiber cable below this radius induces macrobending losses that increase attenuation and, over time, can cause physical cracking of the glass fiber at the bend point.

305 mm (12 in) represents approximately 12 times the cable OD and exceeds the required minimum without being the defined standard minimum value for a completed installation.

381 mm (15 in) corresponds to the stricter bend radius limit - typically 15 times the OD - applied during active cable pulling and installation, not the relaxed post-installation long-term minimum.

457 mm (18 in) is approximately 18 times the cable OD, which greatly overstates the requirement and does not correspond to any standard multiplier used for this cable diameter.

610 mm (24 in) is approximately 24 times the OD and far exceeds the post-installation minimum bend radius requirement, applying no recognized standard multiplier for this application.