I am wiring a NEMA 6-50R as a dedicated outlet for my YesWelder ARC-145DS light service welder (operates off 120V OR 240 V via an adapter dongle). I will be coming off a 40 Amp circuit breaker in a subpanel in my detached workshop. This subpanel is grounded with two 8 feet grounding rods separated by 6 feet using #6 CU wire in series. I have a #8AWG wire set that I want to come off the 40Amp circuit breaker in my workshop subpanel to go to the NEMA 6-50R. However, this wire set has a black wire (hot), a red wire (hot) and a white wire but NO bare ground wire.
The subpanel comes off of a service disconnect box on the outside of my home to the workshop via underground using 8-3 with ground direct burial UF cable (stranded) in a 2 inch non-metallic conduit. Neither the cutoff subpanel nor the subpanel in the workshop have common and ground wires bonded. Can I use the white wire in this wire set from the workshop subpanel to NEMA 6-50R as the ground wire? Should I strip the sheathing off or use green heat shrink tubing on the white wire? I am concerned that using the white wire as a ground violates the NEC bonding of common and ground in sub-panel rules, even though I don't see how it could. Just want to do the right thing!
EDIT: The wire set is labelled: 8-3 Non-Metallic Sheathed Cable Type NM-B 600 Volts E10816K (UL)