Suppose I'm wiring a 100 A subpanel, which receives my two phase wires (black, red/black), my grounded/neutral wire (white), and my ground wire (bare) from the main panel. Since this is a subpanel, the green bonding bolt isn't installed, and so the subpanel neutral and ground terminals are not bonded in the subpanel.
My question is, back at the main panel, are there any constraints on where can I tie the grounded/neutral and ground/bare wires from the subpanel? The main panel has a grounding bar along one side and the usual neutral/ground bars on either side of the breaker rows. Can I connect my grounded and ground wires to any ground/neutral bar in the main panel, since they're bonded in this panel, or must I land the wires from the subpanel on specific bars? Seems like it makes no difference in terms of safety, since neutral and ground are bonded in the main panel and at the same potential, but maybe there's a 'gotcha'. Any advice?
Best Answer
Neutral needs to go to the neutral bar.
The purpose of neutral is to be the normal path for return current which flows as part of the circuit's operation. As such, it can only go to the neutral bar, since only that is rated to handle that current continuously and on a routine basis.
Safety ground certainly can't do that. Think about it, that bonding screw in the main panel, is that a 4/0 AWG screw?? :) No, it's 10-32 and steel, which is a several times worse conductor than copper. That bonding screw was never imagined to handle normal service currents.
That's why you can't land any neutrals on grounding bars and other facilities intended only for safety ground.
Safety ground is not used for anything; it only handles fault currents for the duration of a ground fault (i.e. long enough to trip the breaker). Ergo it does not need to be rated for continuous service current.