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?