Hello I have an old subpanel inside my apartment that is fed by a 30 amp disconnect by the meter in the back of the complex. There are 3 wires that feed the subpanel which are 2 hots and a nuetral that are 10 gauge. There is no ground wire feeding into the sub and there is no ground bar in the sub (way old panel with type T breakers. Seems way undersized for an apartment but it is small. My question is I would like to add a 220 circuit to run a small motor and without having a ground bar in the subpanel and no way to run a ground to either the main disconnect or to a rod outside how would I go about wiring this. Can I run a ground from the new 220 outlet ground screw to the nuetral bus in the sub (i know this is frowned upon)? Or do I add a new ground bus in the panel even though it would not be connected to a ground rod or to the main disconnect? Thanks in advance for the input.