Conductor Stranding: Poor designs lead to breakage.

Conductor stranding is an important component for applications with hi flex cycles or vibration. The higher the conductor stranding the better the resistance to stress caused by flexing. Custom cables with high strand count conductors are the best choice for these types of applications. Higher conductor stranding also makes for an ultra flexible wire when using the right insulation. Discussing the flex requirements with your wire and cable manufacturer is critical to choosing the right cable construction.

Are there circumstances when conductor stranding doesn't help with wire breakage and loss of conductivity? Yes! Recently, I was asked what type of wire I would recommend for an application that required the wire to be soldered onto a PCB. This person was repairing PCBs experiencing conductor breakage at the solder point due to vibration and he thought the wire was to blame. This is a common problem when the wire is soldered onto PC boards especially now with the use of lead free solders.  Applications such as aerospace that are subject to vibration and movement of the wire can cause stress at the solder point.  The problem has nothing to do with conductor stranding or flexibility of a wire, while it is true that high strand conductors and the use of alloy materials adds strength to the conductors. The reason for this has nothing to do with the conductor stranding or how flexible a wire is, but the termination. Termination with connectors is recommended to solve this problem. Cable assembly and contract manufacturers understand this problem and are using edge cards and other types of connectors for termination with newer PCB applications. The problem is more prevalent among legacy boards that are being repaired where retrofitting connectors is usually not an option. Often times a strain relief cannot be installed due to the nature of the application. The solution to repair this type of problem with the old boards may be as simple as using an epoxy to secure the wire to the board to prevent stress at the termination point.

Having the right strain relief is important especially with handheld devices. The lack of or using the wrong type of strain relief can actually cause a stress point and product failure. Strain reliefs can vary in sizes and materials, consult your cable assembly house or contract manufacturer for guidance. I had a customer experiencing conductor breakage on his handheld tool and sent us a sample for analysis. Though his design used high strand count conductor strands, we found the conductor stranding to be damaged at the strain relief, it was discovered the strain relief design had been changed to a spring which caused added strain to the conductors. He changed his design and the returns on his product ceased.

The moral to the story is that though high stranded conductors do resist the stresses of flexing, the cause of the problem may not be in the cable design. Take the time to consult your cable manufacturer and the contract manufacturer for the best material options for your device.