I am trying to connect a 220v 30 amp NEMA L6 plug. There are four wires in the line: red, black, white and copper ground. On the Sub-panel side, the red and black are connected to the two poles of a dual 30 amp breaker. The white and copper are connected to the neutral bar. The wire is 10 gauge. Should the white and copper ground both be connected to ground on the receptacle? Does it matter whether red or black is connected to X or Y on the receptacle?

Ignore the white. Cap it off at the receptacle box. A NEMA6 240v circuit does not require a neutral. Just two hots and a ground.

Red/black to X/Y; colors do not matter.

Red and Black to X and Y doesn't matter.

Neutral and ground should be separate in the receptacle.

The plug cord should have four insulated wires. Black, red, white(neutral) and green (ground). You should not be using Romex for the cord for the plug.

Here is where the confusion lies: Sub-panels usually have separate ground and neutral bars unless they are 3 wire fed.

Let us know if we missed something.

Neutral and ground should be separate in the receptacle.

The plug cord should have four insulated wires. Black, red, white(neutral) and green (ground). You should not be using Romex for the cord for the plug.
KISS, see line #6 in this chart:
http://www.voltec-industries.com/OLD%20VOLTEC%20WEBSITE/OLD%20Voltec%20Website%20Files/images/nema-chart_2.gif

I caught that after I posted, but there was a reference to bare. We were posting about the same time. Thanks.

Thank you both.