Bend Radius

Bend radius is the radius of the tightest curve to which a wire, cable, harness, optical fiber, or component lead can be bent without causing permanent damage or a loss of performance. It is expressed as a multiple of the outer diameter (OD) of the wire or cable and measured along the inside curve of the bend. Standards distinguish short-term bend radius, which applies during assembly, installation, or storage, from long-term bend radius, which applies in the permanently installed configuration.

For cable and wire harness assemblies, IPC/WHMA-A-620 Table 14-1 sets minimum bend radius requirements by cable type — for example, 10 times the OD for flexible coaxial cable — and requires that a harness bundle’s minimum bend radius be no smaller than that of the wire or cable inside it with the largest bend radius requirement. A bend that does not meet Table 14-1 is classified as a defect, though for several cable types (such as shielded and unshielded cable) the table establishes no Class 1 requirement. For installed spaceflight harnesses, NASA-STD-8739.4A Table 7-1 lists both optimum and minimum bend radii, such as an optimum of 10× OD and a minimum of 6× OD for a harness containing coaxial cable or AWG 8 or larger wire. Bending tighter than the minimum stretches and thins the insulation on the outside of the bend, which in extreme cases can expose the conductor, and kinks that violate the minimum bend radius are themselves defects. J-STD-001 and IPC-A-610 apply the same concept to component leads, setting minimum bend radii based on lead diameter or thickness.