litze cable need ground shield?
Both cables need to be twisted. For proper functioning, a shield is not required. However, the cables work as antennae that send a large amount of EMC radiation into the environment. So for your environment it is advised to use shielding. If you don't, your EDM machine will work just fine, however you may loose radio reception near your machine (or similar EMC disturbance problems). It would be best to enclose the entire machine in a Faraday cage, this is however not always practically feasible.