Hi, we are attempting to design a small lab scale stranding machine for the production of small quantities of cabled enamelled copper wire.

A typical cable construction consists of 8x0.236mm strands around a center 0.5mm conductor. All cores are enamelled to IEC 60317-14 to provide a multi-conductor cable. Some other designs are more Litz-like with multiple bundles of 0.1mm wire twisted in hierarchical fashion (type 2 and 3 Litz wire).

We have investigated various designs for stranding machine that could be scaled down to a bench top unit suitable for a lab. One area that is causing particular confusion is that of back-twist and how it relates to the construction of stranded electrical cables. I have seen industrial scale rigid frame and planetary stranding machines, but am confused about what would be the best choice for building our target cables.

Could someone explain the purpose of back-twist and its effects on the cable's properties and how these relate to the design of a planetary stranding machine.