Electrical Behavior of Flexible Cables With Intermittent Faults

This paper presents a study on the effects of flexing on the electrical behavior of motor cables in application to automation and robotic systems. Focus is given to their resistance change from the pristine to the intermittent state. The samples were PVC-insulated 22 AWG wires with bare copper conductor strands. It was found that, under continual flexing, the cable resistance remained small and stable until the intermittent stage, where all the conductor strands were broken. The resistance then increased abruptly by over 40 times and became unstable. Yet, current managed to pass through the cable via the lapped strands. The phenomenon is closely related to electrical contacts under low forces and large displacements. Interestingly, with injected currents as for motor driving, an intermittent cable is "healed" with its resistance reduces drastically. Hence, the cable is still usable. Apart from resistance measurement, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) were applied to examine the broken strands. Traces of arcing were observed signifying (1) the passage of currents across the contacting strands, as well as (2) welding at their contact interfaces.