grounding, neutral,bonded mixed review

In main panel where the main disconnect is located the ground bar and the neutral bar are bonded to the panel… Why does it matter what bar they terminate to? Mixed neutral and ground wires on each? Inspector and I has a conversation about this and he was adamant that they cannot be mixed in this application and need to be corrected, problem is he couldn’t explain why and the way I learned was that its fine in this application … Lay some wisdom on me guys

If there one bar for both EGC’s and neutrals there isn’t a problem. If you have a separate EGC bar bonded to the panel enclosure then only EGC’s can terminate there. You cannot use the enclosure as a path for the neutral current. From the NEC:

Ok so if there are two bars yet they have a direct bonding by a copper flat bar they can be mixed but if the two bars are only bonded by way of being connection to the panel then they must be separated, one with direct ground connection for grounds and the other for common? Is this correct ? And the reason is stated above in 200.2b based in continuity? Is the explanation because if the connection to the panel fails the common could become ungrounded thus make the panel live?

The basic premise is that all metallic parts and EGC’s carry no current under normal operating conditions which would help to eliminate the problem that you’ve mentioned. Although not directly related this graphic from Mike Holt kind of outlines the problem.