Basic: The function of the insulation crimp – on the example of a B-crimp

During crimping, a predetermined breaking point (3) is created at the transition between the solid crimped stranded conductor of the wire crimp (1) and the subsequent flexible stranded uncrimped conductor (2).

Vibrations can cause the cable to swing open and stress this predetermined breaking point (individual strands breaking off from the stranded conductor).

Example: Swinging open (A) of a cable with a soldered connection (B)

This predetermined breaking point (3) is primarily relieved by the “rear bellmouth” (4) (which is absolutely essential).

Further relief is provided by the insulation crimp (5). By fixing the insulation, this prevents the cable from swinging open and thus mechanical stress on the predetermined breaking point. (Other ways of relieving the predetermined breaking point are, for example, bundling the cables after the connector housing, cable ties, shrink tubing, etc.).

In order for the insulation crimp to fulfill this task, it must meet the standard specifications:

At least 1/3 or 120° (A) of the insulation circumference must be covered by the crimp flanks. The ends of the crimp flanks may penetrate the insulation, but not pierce it. No damage to the individual wire strands is permitted.

If the crimp flanks pierce the insulation, this area (6) is cut open.

Insulation material has different properties, for instance hardness. In the case of brittle insulation, the insulation “bursts” right up to the end of the wire (in the direction of the wire crimp).

The adhesive force of the insulation on the stranded wire composite also varies. I.e: While one insulation can be easily moved on the stranded conductor, other insulations literally “stick” to the conductor strands (which does not make the stripping process any easier).

If the insulation has burst open to the end of the cable and is subjected to a tensile load with a lower adhesive force, it can be pulled out of the insulation crimp (7).

In this case, the insulation crimp cannot fulfill its function. There is also a risk that the uninsulated stranded wire assembly (8) will be visible at the end of the connector housing.

Under which conditions is the insulation of a cable subjected to tension? A few examples: When handling pre-assembled cables, when assembling individual cables to form a wire harness or when the cable is kinked directly after the crimp contact (or connector housing) during final assembly (laying the wire harness).

And by the way: “No need for an additional wire crimp by dipping the insulation crimp flanks into the stranded wire! One is completely sufficient! ” 😉

Conclusion: Lots of “ifs” and “buts”! What may not matter or be tolerable in one application may well be the reason for failure and an expensive complaint in another.

The basic requirements should therefore always be adhered to. If this is not possible because (for example) the insulation crimp flanks are too long and no suitable crimp contact is available, then there is still the possibility of a special release for this insulation crimp. Of course, only after verifying whether this suboptimal or poor insulation crimp might have negative effects on the crimp connection in the application.