I installed a subpanel when I switched from an electric stove to gas. I used the 40A 220V breaker that formerly served the stove to power the sub panel. The cable is #4 with two conductors and a ground. I have 6- 15 amp breakers in the panel providing branch circuits for my kitchen and other areas of my house. The grounds and neutrals all share the common bus bar in the sub panel. Everything has worked fine for years now. Can someone explain why I read that ground and neutral are to be isolated in the sub panel? Please don't answer because of the NEC since that does not explain why. What is the risk of my current situation?