I added a bar to a existing cabinet once. The added bar and existing
bar both had spots for 12 gauge or smaller wire.

Plus each bar had significantly larger spots for heavy conductors.
perhaps a electric stove or something like it

So added 2 copper heavy tie lines between the old and new bar,
figuring that would never cause a problem plus the bar was bonded to
the cabinet

I had to get middle states to reinspect the cabinet for home sale, the
inspector complimented me on my good job........

the existing bar had issues many of the screws were like welded on
place, they must of been overtightened at one time and the heads would
break off when loosened. i had ven tried heating some. the quick
project took all day