Wiring A Welder Dedicated NEMA 6-50R With #8 Wire Set Having A Red, Black And White Wire With NO Ground

Question

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)

Answer 1

With #6 or smaller wires, NEC requires you to use the correct native color wire. No "remarking to change purpose" is allowed, with a solitary exception: in manufactured cable, white can be remarked to be a hot.

So, no.

However there is another concern: you must use one of the approved types of wire and cable. Approved /3 without ground has not been made for many decades. Therefore this is either a cable type not allowed for AC power, or, it is so old that its safety is questionable. If you can state the labeling on the edge of the cable, we can tell you what you have.

Lastly if wire cost is a concern, select a NEMA 6-50 receptacle listed for aluminum wires and 75C temperature. (The breaker already is). At that point you can use #6 aluminum, good to 50A @ 75C.