Strain Relief

Strain relief is a connector device or accessory that mechanically secures the cable or wire bundle to the connector, so that mechanical loads — pulling, bending, vibration — are carried by the hardware and the connector body rather than transmitted into the electrical terminations. NASA-STD-8739.4A defines it as “a connector device that prevents the disturbance of the contact and cable terminations,” and IPC-HDBK-620 describes it more plainly as “a type of accessory which clamps wires for support.”

In practice strain relief takes several forms: backshell clamps, strain relief clamp adaptors, strain relief boots, and — on insulation-displacement (IDC) connectors — integral primary and secondary strain relief features that latch onto the cable jacket and wire insulation. A backshell commonly provides strain relief as one of its functions. For the clamp to work, its size should match the outside diameter of the harness; where the bundle is too small, standards call for building it up with tape, sleeving, or a grommet so the clamp can grip properly.

Strain relief should not be confused with stress relief, which NASA defines separately as the formed length of conductor left between terminations to minimize stress. During assembly, workmanship standards require that strain relief members (clamps and backshell tongs) not be stressed or forced to rotate, and that they be torqued to the values stated in the engineering documentation.