my recent post about a sub panel in attached garage was answered and i am wiring as instructed but dont understand the concept of why i need a seperate ground and neutral wires and ground and neutral bars in the sub if they are both wired to the same ground bar in main panel. help me understand this. thanks
I will expand the other explanation.
1) The neutral carries current back to the transformer so the neutral in your sub panel is connected to the neutral in the main panel.
2) The ground is not supposed to have current flowing in it except in a fault condition.
If the ground wire and the neutral wire were connected in the sub panel as they are in the main panel then the neutral and ground would each be carrying a portion of the return neutral current. There is a lot more theory to it but in a nut shell this is the reason.