"....Hi, I am new to this forum and glad to be a member. First of all I have to explain how I usually do when wiring up a step down transformer(600v/120/208v).The transformer is bolted to the floor.I will run the 600v wire (3 hot)to the primary side H1,H2,H3 and the secondary cable(3 hot and a neutral) X0,X1,X2,X3to the panel. Then I will run a bare or green copper wire and connect one end to the building main cold water pipe and the other end to the ground lug (X0)of the transformer. Also the secondary neutral cable is connected to the same ground lug as well.
Now What happen if I have to wire up a transformer that is on wheel and is portable. The reason is that in my factory there are 3phase 30 amp 600v outlet everywhere and we need 120v and 208V power. So the idea is to plug the transformer to the 600v outlet and we have 120/208v power. My question is that how should I ground this setup. There is of course a ground wire from the 600v outlet. Like I mention before I will run a ground wire to the cold water pipe if the transofrmer is in a fixed location. Now since the transformer and panel is portable, All I can do is to connect the ground wire from the outlet to the ground lug in the transformer. And connect the secondary neutral to the same lug. in other words, all ground wires are terminated at the X0 that bond to the frame of the transformer.Is this correct and safe? .."

I am using extra hard usage cable to make a 30amp plug which is wired into a 30A fusible disconnect and from it into the 15kVA transformer. The 120/208V secondary then go to a 150A 3 phase panel.

From the code book, #8 copper shall be used as the ground conductor for the secondary side; however, the ground conductor from the 600v outlet,which I am using for everything, is only #10. Therefore, is it safe? If not,what can I do to make it safe? Thanks in advance.