Bending Radius of Cables when installing

In cable talk, ‘bending’ is the positioning/flexing of cable when it is under tension. When installing a cable, the objective is to limit the mechanical forces acting on the cable so that its physical and electrical characteristics are maintained throughout its expected service life. An important aspect of this is a cable’s specified bend radius, which is a measure of how tightly the cable can bend without suffering any permanent damage.

Nonshielded cables can withstand tighter bends than shielded cables. This is especially true for cables with helical applied metallic shielding tapes. If these tapes are bent too sharply, they can separate or buckle and cut into the insulation.

As shown in the above table, minimum bend radius is generally specified as a multiple of the diameter of the cabling being bent. This figure is measured at 180 degrees of bend, i.e. when a cable is bent entirely backwards and is parallel to itself. If you do this bend and the two parallel sections of cable are closer to each other than the specification shows (4x to 12x the overall cable diameter, in the above table), you’ve likely damaged the cable and its performance is no longer guaranteed.

The minimum bending radii shown in the above Table are in compliance with NEC 300.34 for cables rated over 600 V, 330.24 for Type MC cable, and NEC 336.24 for Type TC cable. The values shown for other constructions are not defined in the NEC and ICEA recommendations.

Since UniShield is a unique construction, there are no applicable values for the bending radius in the NEC, however, in accordance with ANSI/ICEA S-93-639/ NEMA WC 74-2000, the recommendation is 8X for single conductors and, for multiplexed or multi-conductor cables, 8X the diameter of an individual conductor or 5X the overall diameter of the cable assembly, whichever is greater.