The Necessity of Strain Relief: Backshells and Cable Clamps
Mechanical stress is the primary cause of connector failure. We discuss how to use backshells and cable clamps to transfer the load from the delicate pins to the robust connector housing.
Mechanical Integrity: The Role of Strain Relief
Even the best electrical termination will fail if the wire is allowed to pull, twist, or vibrate at the point of contact. Strain relief is the mechanical practice of ensuring that any external force applied to the cable is absorbed by the connector's shell or the device's enclosure, rather than the tiny metal pins inside.
1. Backshells: The Professional's Shield
In circular and D-sub connectors, a backshell is a metal or plastic housing that screws onto the rear of the connector.
- Function: It provides a solid "grip" on the cable jacket. It also provides an area to terminate the cable shield (braid) to ensure 360-degree EMI protection.
- Types: Right-angle backshells are used to reduce the profile of a connection in tight spaces, while "environmental" backshells include O-rings to prevent moisture from entering the back of the connector.
2. Cable Clamps and Glands
For wires entering an enclosure, a "cable gland" provides both a seal and strain relief. By compressing a rubber grommet around the cable, the gland prevents the wire from being pulled out of the internal terminal blocks. Without this, a single accidental trip over a cable could rip the wires directly off the PCB, leading to a costly and time-consuming repair.
