I'm preparing to provide new wiring to a sizable addition to a log home. Prior to beginning the new work I mapped my existing circuits thinking it best to correct any potential overloads in the existing panel/circuit design before introducing any new problems on my own.

Decided to make a few changes by running 3 new 20 Amp dedicated circuits to service a garbage disposer, a microwave, and a utility room with a washer/dryer (gas) - all are currently on shared circuits. I was surprised when I opened my main service panel and found that neutral and ground wires from existing circuits are interchangeably attached to either the neutral or the ground bus. In many cases both the ground and the neutral from a respective circuit are attached to one or the other of the buses under under the same screw.

I have read that the ground and the neutral bus are generally bonded within the main service panel. Does this mean that there is really no difference between the ground and neutral bus within a main service panel? If I add circuits can I simply connect the hot to the breaker and both the white and bare copper ground to one or both of the neutral/ground bus?

I expected things to be far more orderly.

The neutral and ground are connected together in a main panel ONLY if the Main Breaker is in that panel. There can be a main panel with the Main Breaker elsewhere,such as outdoors, in this case the neutral and ground is noit connected, or "bonded" together in the panel.

The reason is that wherever the Main Service Disconnect is located is where the Neutral is grounded with the ground wire that goes to ground rod(s) or city water.

Now the two wires under one screw may need to be changed so that there is only one wire per screw. Look on the panel dor for a lable that explains if the ports on the neutral/ground bars are rated for one or more wires.

That really didn't answer the Original; Posters question. They want to know, given that this panel is already electrically bonding the ground and neutrals of the branch circuits; is it a violation of the NEC for the respective circuits to have their ground and neutral conductors terminating on GND and neutral buses indiscriminately. IE. There is no clearly defined Neutral or Ground bus.

Of all the electrical work I have come across only the main breaker box has the two bonded and only one wire per screw. Also, in my area at least, the inspector wants only neutral (white) on one side and bare ground on the other to prove all the circuit connections, even though they are still connected with either a connector beam or just a green bond bolt.
Ever take a look at your drop power coming in to your house? The bare one coming in becomes the neutral and is grounded (usually from the meter box) outside the house/bldg as well before it goes into the main breaker box where is is bonded to the neutral bar. Hope this helps some.

Just a heads up to the new guys, please read the OP date--the original post is almost three and a half years old.

A meter is more than 10' from the panel, should you ground the neutral or separate the ground & neutral,& where in the code do you find that

It is not that easy to find it, besides. It depends on where the Main Service Disconnecting Means is located.

Sounds like the issue is if the meter is ten feet or more away from the meter, is when the Main needs to be located at the meter, and then a separate equipment ground is needed from Main to panel.

Ten foot happens to be the popular unwritten rule of max distance from meter to panel, then the Main must be at the meter, then the neutral and ground must be separated at the panel.

Does this sound like your situation?

Who told you about the 10 foot?

It's in the code 4 MD,DC & Va

That is a local code to quantify the distance. The National Electric Code states the Main shall be immediately as the service entrance feeder enters the home.

To read the actual code in those states you will need to consult with the state electrical inspector.