Hi - I repaired a broken laptop power cord last night. The cable consisted of a center conductor with PVC insulation and then a braided conductor around the outside of the PVC, and then a jacket on top of that braid.
The braid had completely broken due to (I'm assuming) excessive flexing. It broke right at the connector's strain relief.
What was interesting to me was that the broken strands were all covered in a gray powder that rubbed off on my fingers. What is this material and what reaction causes it?