trogman wrote:Is your concern that the rope would break in the case of a sudden loading with a short fall? I suppose that makes sense, but a 5K strength rope is not likely to break in such a situation, even though it is static. I'm pretty sure the ascender would cut the main rope in two before the tech cord breaks. If fact, the danger of an ascender cutting the rope is one reason NOT to use one where any significant fall factor is a possibility.
Am I missing something here?
Yes, you're missing something. It's not just about the rope breaking at its 5K *STATIC* MBS, it's about a shock load being absorbed and how that peak force is spread between the rope, the knots, the hardware, the harness, and the body. And as you said, potentially through an ascender clipped to a static rope.
If you have access to copies of Alpine Caving Techniques, On Rope, Vertical, Life On A Line, and other definitive vertical caving publications, read up on what they recommend for cowstails and ascender tethers. Also note that best practices for rock climbing and mountaineering adamantly insist on not using Spectra or Dyneema etc cords/webbing in any life safety application that could see a sudden shock load, for the same reasons.