Single Strand Copper Wire For Buss Bar, Is this OK?

One of the areas I get an occasional question on has to do with what you see in the photo above. You are looking at the backside of a fairly typical electrical panel. What you see is three rows of standard two pole circuit breakers and the master wire harness coming in from the top side with all of the DC positive conductors attached. On the opposite poles you see some neatly bent uninsulated single strand copper wire that connects all of the other poles on the circuit breakers. At each ...