Minimum bend radius is the smallest allowed radius the cable is allowed to be bent around. While cabling, these cables are bent in many different directions when going through conduits and when pulling around a sheave.
Cables are composed of different components and if bent too far you may put too much stress on those components to the point of damaging them. For example, a 6 strand indoor fiber optic cable if pulled too hard around a tight 90 may appear to be fine once the cable pull is finished. Unfortunately, what commonly happens is the stress around that 90 caused the individual strands to break under the jacket. To prevent this kind of damage, cable standards such as The National Electric Code (NEC) and the Insulated Cable Engineers Association (ICEA) formed requirements for minimum bend radius.
How to Calculate Minimum Bend Radius.
The figure above shows a cable with an outer diameter of 2 inches being bent around a radius of 12 inches. The minimum bend radius is based on the diameter of the cable and the type of cable. The following formula is used.
Minimum Bend Radius = Cable Outer Diameter x Cable Multiplier
Cable multipliers are determined by industry standards and vary from cable to cable. When purchasing a cable, check the spec sheet, many manufactures have the minimum bend radius provided to you for each cable part number.