Importance of Following the Directions
Today’s performance requirements for Material Handling connectors and cables are being pushed to the limit based on the requirements of Fast and Opportunity Charging. The demands for higher amperage and voltage using wires that maintain flexibility and connectors that are as small as possible require that the cable preparation and attachment of contacts is absolutely per specifications. In many past applications, customers often used connectors/wires that had greater performance capability than the application required (imagine using a connector rated to 350 amps when the application required 250 amps) allowing the crimping to be outside specification and still perform as required. Today, applications are pushing the 350 amp connector to 500 amps or more.
In this article, we are going to discuss the three key attributes of connector performance that are directly impacted by the proper crimping of contacts.
1) Wire Retention:
To assure that the wire is retained properly when crimped in a contact it is critical that the correct contact, crimp tool, die set, and wire selected is per manufacturer’s specifications. It is not a safe assumption that all tools and dies designed to crimp one manufacturers contacts on a particular wire will also work properly on another manufacturers contacts designed for the same wire. Contacts from different manufacturers can vary based on the outside and inside diameters of the crimp barrel.
Tools that have a fixed amount of movement (scissor or wrench type crimp tools are good examples) may not allow sufficient depth of the crimp allowing the wire to be pulled from the contact. Other times, it can allow over crimping causing wire strands to break or contact barrels to crack. When this occurs, it not only reduces pull out force but also the electrical performance, as fewer wire strands are carrying energy to and from the connector interface. Contacts that develop cracks once again reduce mechanical and electrical performance and may allow shorts to occur. Crimp tools that continue crimping until a certain physical “resistance” is achieved before releasing have a wider range of user ability but still must be sized within reason and per manufacturer’s recommendations.
Lastly, it is critical to choose the proper wire/contact combination. Using a larger contact than the wire used and over-crimping can lead to all the issues described in section 2 and 3 below. If you have no option, then soldering would be the preferred attachment method in this situation. Removing strands from a wire to fit into a crimp barrel that is designed to accommodate a smaller wire can also lead to failures. Lastly, although obvious, trying to achieve performance that the wire itself is not specified for will cause the connector to fail regardless of crimp and cable preparation. Sizing of the conductor for the load and ambient operating temperatures per NEC of other IEC guidelines is the starting point for long reliable field service life of equipment.
2) Contact retention:
An incorrect crimp may cause contacts to fail to insert properly in a connector housing. All contacts have a retention feature that prevents them from dislodging from the outer housing when reasonable force is applied. Incorrect crimps may distort this feature to the point that the contact does not latch or achieves only a partial latch. In some cases, an incorrect crimp can cause the crimp barrel to bow like a banana preventing the contact from inserting far enough to reach the latching mechanism (often a spring). In this case, the contact may achieve a press fit in the outer shell fooling the assembler into assuming it is latched. However, this will quickly dislodge during mating in operation leaving operators exposed to a live wire.
3) Contact Performance/Wear:
It is very important that the crimping operation does not distort the angle of the contact interface that may cause either higher or lower mating force or cause the contacts to be damaged. In all cases the barrel and contact area should maintain co-planarity with the crimp barrel within manufactures recommendations. With blade style contacts, performance depends on the pressure (or normal force) of the two contacts against each other during mating. If one blades is distorted, it can increase the force causing premature wear and in extreme cases stubbing of the contacts causing one or both to try to dislodge from the connector. If distorted in the opposite direction, it will cause reduced normal force leading to increased electrical resistance and potentially intermittent arcing. This arcing can lead to a connector melting and in some cases cause a fire. With pin and socket style contacts, an incorrect angle can cause stubbing of the contact typically leading to a damaged tine on the female socket or once again increase in wear and poor electrical performance after repeated mating cycles.
This is even more critical when a connector with a bad contact is mated to multiple other connectors (envision a charger connector being used to charge multiple devices) as the damage can spread from the charger connector like a virus to impact all the connectors it is mated to during daily operation.
In summation, the best way to ensure the connectors perform to expectations is to assure the manufactures recommendations for correct assembly is used. The manufacture carefully chose and tested these connectors for your application. It is also important to note that many safety agency approvals are based on the tooling used during testing. Using incorrect tooling can inadvertently negate the approvals your systems require.