Helped out a fellow sparky today on a remodel job. Panel was full, added a few mini breakers. The neutral bar was also full so he installed another ground bar. He connected the egc's and neutrals to this bar. This is in a service panel where the main ground bar is bonded to the panel. He insists it's ok but I don't think so. I have never thought about doing this so I haven't given it much thought. Ok guys discuss!
Gentlemen: If it's the main panel, with the main disco, then that's where the neutral is bonded to the ground conductors, correct? If you are adding another termination bar (neutral/ground) the bar you are adding should (IMHO) have a jumper connected to the "factory" bar. The "jumper" should be sized according to the incoming neutral that is connected to the "factory" bar.
If it's a sub-panel, then there has to be a "ground" bar, and an "isolated" neutral bar, with a "ground" and "neutral" conductor for each.
If the "added" bar in your scenario is "mounted" to the panel enclosure, then you are using the panel enclosure for a "neutral & ground connection back to the "factory" bar & bond. The current passing through other "grounds" depending on the resistances. Not Good.
Hopefully my explanation above is clear enough to understand. John
The problem is that the branch circuit neutral current is forced to return to the bond point through the enclosure of the service, even though we're only talking about half a foot or so. This applies to each neutral that is connected to the added ground bar.
That "half foot or so" of sheet metal can't be a neutral, even though its the service disco.
My Square D info says that the add-on bar is for equipment grounding ONLY. The factory installed neutral bar(s) are required to have a minimum number of terminals for landing neutrals based on the number of circuits the panel is arranged to supply. Where there are a large number of equipment ground conductors they MAY be landed more than one to a terminal IF the panel is so listed (and marked) OR an additional bar kit must be installed. Terminals used for equipment grounding are treated differently than those for neutrals because the connection does not undergo the cyclic loading and expansion/contraction of the current carrying neutral.