I added a sub panel next to the main entrance panel. I linked them with Romex 6/3 plus ground using a 50amp breaker on the main panel. I understand that the ground and neutral in the sub panel must be separated. In order to ground the sub panel and link up the ground wires in the sub panel circuits, I use the ground wire in the NM-B Romex cable coming from the main panel. The problem is that the ground wire in the 6/3 Romex cable is 10 gauge solid. Should that ground wire not be 6 gauge like the other 3 wires?