Hey bobspryn,
curly cables are usually made to accomodate a varying length (e.g. when using an electric shaver), but this is usually not how cables for permanent and repeated motion look like. Here in this case I would check if the inner wires of the curly Z cable break invisibly where they come out of the fixed plastic parts. That is where they are subject to their biggest stress. I would check here first, at least if the machine is not totally new. If it is new, I would rather think of the connectors, or the motor sockets, or EMI, e.g. as mentioned here or here.
What I mean with cables made for permament motion are those made for moving machine parts like found on CNC machines and other aumomation machinery, e.g. IGUS chainflex® flexible cables for movement or LAPP Power and control cables for power chains, like e.g. shielded LAPP ÖLFLEX® CLASSIC FD 810 CY that I bought for my spindle. Here an image of this cable:
For a stepper motor, I would of course use a thinner shielded 4+PE, instead of this thick 3+PE).
Many people here built their drag chains for Onefinity with these cables, you can find files to print 3D parts for free on the web and even in this forum.
Sure. The cables mentioned above are made specifically to be moved all the time, 24/7 for years. But it’s not only the cable, it’s also how it is laid to perform a certain movement and have their strain relief at each axis end and beginning. The problem with the curly cable is, you could say, as a hobbyist, it should last long enough, I’m not running it longer. The problem is, it is stressing the cable end because it is hanging around and you don’t know when it will be that it could fail, but it happens that it fails and it is offered as replacement part, and I am sure that a hobbyist can get more angry then than a professional that computed the expected lifetime of their power chain at installation time and exchanged the cables after a specific number of years.
The cables mentioned above are not expensive, many hobbyists use them. Hope I could help!