An installation crew is pulling an optical fiber cable into a riser. The cable has an outside diameter of 25 mm (1 in). As the cable is being pulled off the reel and through a pulley into the riser…

254 mm (10 in) equates to approximately 10 times the cable OD, which is below the required 15x multiplier and would violate the minimum bend radius during pulling, risking fiber damage.

Industry standards specify that the pulling sheave (pulley) diameter must be a minimum of 15 times the cable outside diameter to avoid exceeding the cable's minimum bend radius during installation under tension. For a 25 mm OD cable: 15 x 25 mm = 375 mm, making 381 mm (15 in) the correct minimum sheave diameter to protect the fiber from microbend and macrobend damage during the pull.

508 mm (20 in) exceeds the minimum and is acceptable in practice, but it is not the minimum required - the question specifically asks for the minimum allowable pulley size.

635 mm (25 in) is larger than necessary and does not represent the minimum required sheave diameter for a 25 mm OD cable.

762 mm (30 in) is well above the minimum requirement and is not the correct answer when the question asks for the minimum allowable pulley size.