Undercrimping

Undercrimping is a defect in crimped electrical connections where the conductor is not sufficiently deformed within the terminal during the crimping process. This leads to inadequate electrical contact and reduced mechanical grip, increasing resistance and the risk of loosening, vibration damage, or corrosion. Undercrimping can affect a range of terminal types, including butt splices, ring terminals, and lugs, and is a reliability and safety concern in automotive, aerospace, and industrial wiring.

Causes of undercrimping include using an incorrect terminal for the conductor size, employing the wrong crimping tool or die, and insufficient conductor preparation (for example, insulation positioned too close to the crimp). Other factors are incomplete conductor insertion, damaged or nicked insulation, and attempting to reuse worn tools. Visible signs may include gaps between the terminal and conductor, incomplete strand capture, or insulation not being captured by the crimp.

The effects of an undercrimped joint can be elevated contact resistance, localized heating, intermittent connectivity, arcing, and eventual connector failure. Moisture and corrosion can further degrade a marginal connection, and vibration can cause a weak joint to loosen over time.

Detection and prevention rely on visual inspection, pull testing, and verification of crimp height and other specifications per applicable standards and manufacturer guidance. Preventive measures include selecting the correct terminal and wire size, preparing the conductor properly, ensuring full insertion, using the correct calibrated tool and dies, and avoiding re-crimping on a single joint. Standards such as IPC/WHMA-A-620 provide guidance for acceptable crimp quality in wire harness assemblies.