Yeppers your question has been discussed and cussed on here many many times in the 15 + years I've been lurking here, but it remains in my opinion a good legitimate very reasonable question, so here are my professional although "rusty" (been retired from AC Power Distribution EE practice 20+ years) comments:
WARNING AND DISCLAIMER when in doubt consult with local authority and utility providers and local competent trained Electricians and Engineers versus lay Billy Bob or even professional (including mine) opinions posted here. Electricity can be dangerous to your home or life so use care!!!!!!!
YOUR QUESTION: In a new panel is the neutral bar and ground bar connected?
ANSWER YES (if its the Main service entrance panel) AND NO (if a sub panel fed from the Main)
ONLY at the main service is the Neutral Buss connected to the Equipment Ground Buss. In laymens terms, if your house has a typical main breaker equipped service entrance panelboard YES the Neutral and Ground Busses (if it indeed has two separate busses) are electrically connected. It would be possible the panel only has one buss to which BOTH the (White) Neutrals (GrounDED Conductors) and the Bare/Green (Equipment GroundING Conductors) are attached which accomplishes the same thing. If the panel has say a Buss on each side and itís to be used as the main service entrance, thereís a tie bar that bonds the busses together, while if itís for use as a sub panel, they would NOT be tied. Also the outer metal case/frame of the panel, being a non current carrying conductive enclosure, requires a bond to the Equipment Ground, so thereís a screw through the buss to the case frame that accomplishes that.
EARTH GROUNDING OF THE NEUTRAL (i.e. itís a GrounDED Conductor unlike the Hot UnGrounDED Conductors)
In all the jurisdictions in which I practiced, the incoming Neutral from the utility was earth Grounded at one of three locations: 1) The weatherhead riser where the incoming Utility Neutral attached to the customers Neutral down to his panel; 2) Inside the Meter Base; 3) Inside the main service entrance Panel. The Neutral is connected to mother earth by means of a GroundING Electrode Conductor (No 4 bare copper wire) that leads to a GroundING Electrode such as a "made electrode" of one or more copper rods driven into mother earth and/or other suitable GroundiNG Electrodes such as buried metallic pipes or structural or foundation steel etc. etc. YOUR QUESTION
In the 1950's panels where you did not have a ground bar, how would you run a ground wire,or what would you ground to? Can you ground?
In the "old days" if a home was equipped with typical in those days maybe a 60 amp (maybe a 100 amp panel in later years) 120/240 volt single phase three wire service, there were still (same as today) three wires from the utility transformer, 2 Hot UnGrounDED phase conductors L1 & L2, and the Neutral GrounDED Conductor. Those old small panels or fuse boxes only had one buss that the outgoing home branch circuit Neutral conductors were wired to. NOTE the incoming Utility Neutral would still be earth grounded similar to the above. You only ran 2 conductors (Hot and Neutral) to the 120 volt receptacles as they were only two wire devices, 2 pole 2 wire UnGrounDED. There was no provision in the branch circuit (only 2 conductor) wiring or the receptacles (only 2 pole) for the third safety Equipment GroundING conductor as used today.
If you wanted to convert to a modern 3 wire branch circuit (Hot UnGrounDED Conductor,,,,,, Neutral GrounDED Conductor),,,,,,Equipment GroundING Conductor) you would have to run 3 NOT just 2 wires to the receptacles and the receptacles would be two pole three wire GroundING type NOT the old 2 pole receptacles.
The incoming utility Neutral is bonded to mother earth at one of the three locations I described above and at the main service entrance the Neutrals and Equipment Grounds (if so equipped) are effectively bonded, its just that in the old system you didnít run any third safety ground wire out to any 3 pole receptacles as done today, but if you did, the bare/green Equipment GroundING Conductors would wire to that Neutral Buss in an old panel. Sooooooo you could upgrade an old 2 wire system to a modern 3 wire, its just the Neutrals and Grounds would BOTH attach to that single common Neutral/Ground Buss similar to a modern panel that had only one common Buss where BOTH Neutrals and Equipment Grounds were attached. What makes a modern 3 wire safety grounded circuit different is the use of three conductors (Hot Neutral Ground) to 2 pole 3 wire GroundING type receptacles NOT SO MUCH the main service entrance equipment (old or modern). What matters is that the third safety GroundING Conductor has a return current path back to the panels Neutral (be it one common buss or two that are tied together) FOR FAULT CURRENT RETURN SO THE BREAKER TRIPS.
The Equipment GroundING Conductor provides a separate dedicated low resistance normally NON current carrying path for FAULT CURRENT ONLY, NOT the normal return current carrying like the Neutral provides.......
Iím sure I missed something and if I did I hope the more current still practicing fine electricians here can add to or correct this, were never too old to learn I figure.....So enlighten me pleaseeeeeeee
Ol John T and all