i'm replacing an old 220v receptacle in my shop with a new one that mates with a plug on a dust collector i just got. when i removed the existing receptacle it had two hot wires, a neutral, and no ground. when i went to add the new receptacle, i observed it takes two hot wires, a ground, and no neutral.
the wiring all goes through 1/2" metal conduit that connects directly to the sub panel. the sub panel is connected to a larger piece of conduit that runs through the ground to the main panel in the house.
none of the other outlets in the shop seem to be grounded.
what's a safe way to connect this new outlet that requires a ground?
a) connect a bare copper wire to the outlet box, allowing the conduit to act as ground
b) connect the neutral wire to the receptacle's ground, since it eventually grounds at the main breaker
photo showing inside the sub panel, wires connecting this circuit identified by green circles:
photo of the new receptacle that i started installing before noticing it has a ground and no neutral: