In the main service panel, take note of how the grounded and grounding bus bars are linked. This implies that they may be regarded a single bus bar electrically. This implies that both grounded (neutral) and equipment-grounding cables can be terminated on either bus bar. It also means that if you were to remove one of these cables from its connection to the panel, the other cable would still be properly connected to the panel and functional.
The linkage between the two bus bars is usually made with a screw or bolt that passes through both bars. This ensures that even if one of the cables is removed, the other cable will remain connected to the panel. However, this linkage does mean that both cables must be able to slide through the conduit or wireway to reach their destinations. If this is not the case, then at some point during the replacement process one of the cables will be left behind in the conduit or wireway.
Also take note of where the ground bus bar connects to the panel. This is typically done using a metal connector plate attached directly to the metal frame of the panel. This means that the ground bus bar cannot be separated from the panel without first being removed from the metal frame.
Finally, check the bonding of the equipment grounding conductor to the chassis or body of the device it grounds. This should always be done after any work has been performed on the device that might have affected its electrical connections.
The neutral bus bar The bar connects to the main service neutral and returns the current to the power grid. The neutral bus bar, which also functions as the grounding bus bar in many service panels, is where the individual bare copper circuit ground wires are terminated. It should be either metal or plastic and should not contain any oil or other conductive material that could cause shorting.
The function of the neutral bus bar is to connect the main service conductor to the metallic structure of the building to provide a common reference point for the electrical system. This allows you to identify which side of the meter is positive and which is negative when there is a voltage difference between them. The term "ground" will be used from here on out to describe this same function.
Since the metal frame of a house is usually the closest thing to a true ground, it makes sense that we would want to connect our house to this metal frame via a ground rod or wire. A ground rod is an extension of the metal frame of your home's foundation that is connected to the meter base plate or some other highly conductive surface such as a metal pipe located deep beneath your yard soil.
If the main service panel is also where the grounded (neutral) conductor is attached to the grounding electrode, then combining grounds and neutrals on the same bus bar is not an issue (as long as there is an appropriate number of conductors terminated under each lug). Combining grounds and neutrals on one bus bar increases the risk of a short circuit if they are not properly separated. For example, if the combined ground wire gets pinched at any point, it could create a path from the metal body of one appliance to the metal body of another appliance through the power line.
If these two sets of wiring were on different buses, there would be no problem. But because they're on the same bus, there's no way to tell which conductors are neutral and which are ground unless you do some sort of identification process first. For example, if all the grounds were tied together, then you would know that any current flowing into them must be the result of a fault somewhere in the system. You would then need to identify which outlet was responsible for sending current into this group of grounds before you could fix it.
The neutral bus bar is connected to the ground at the service panel (just at the service panel—this is critical). As a result, the ground lead and neutral should be connected to the same bus (the neutral bus bar). Any sub-panel following the principal service from there, however, MUST have an isolated neutral. This means that the neutral bus bar for these panels will not connect to the ground bus bar at the main service panel.
Is the neutral bus and third-phase bus the same? If so, they must be connected to each other and to the third-phase conductor.
If they are not connected, then you have mixed phases on the system. This is OK if you are only using single-phase equipment, but it can cause problems if you have three-phase appliances such as heaters/air conditioners/refrigerators/freezers. The reason for this is that most three-phase appliances use all three phases equally to operate properly. For example, if you have three-way power strips used by multiple appliances, then they must be equipped with separate neutral outlets or the power strips will confuse which terminals are being used by which appliances.
It is important to remember that if you have mixed phases (neutral and third phase present), then any device that is not dual voltage (i.e., accepts 120 volts or 240 volts) may be damaged by excessive currents due to the presence of the third phase.