The issue of busbars with holes reducing the ampacity of the busbar has captured my interest. It occurs to me that calculating the cross-sectional area at the hole and using that to determine ampacity ignores the fact that it's not an empty hole. The hole is covered by a copper lug which replaces some of the area lost to the hole. Let's say the busbar is 20mm wide by 6mm thick. That's 120mm of cross section. Drill an 8mm hole and you've reduced the cross section by 48mm, but the lug would add back around maybe 16mm of copper so the reduction is only 32 sq mm. And right beside the hole there is more than 120 mm of cross section because there is the added area of the lug. Perhaps 32 sq mm. So how much of a reduction in ampacity does the hole plus a lug actually require? I'll bet it's not very much. Ampacity is determine by temperature, and copper is a good conductor of heat as well as electricity, so yes, maybe the slice right at the hole gets hotter, but there is additional material right next to it to help absorb the heat.
I don't know what the literature says about this. I'll be checking into that.
Interesting idea you have here,
Haysdb 
If the bus bars have large safety factor, there should not be much of a problem. If not, everything counts.
In my case that I use hose clamps + battery stranded wires to wrap around round busrods do not have this problem. No holes drilled, no lugs (normally a bit small for the amperage, even with the correct size = a bit warm at high amps), no worry. Plus the clamping force for each hose clamp should be adequate at ~100 lbs for each 1" round, 8-mm (~5/16") wide clamp. I use 3 * SS304 clamps per joint.
I googled clamping force with normal SS304 hose clamp and found this below. Even at 50% of this value for safety, 50 lbs clamping force for each clamp, and I intend to use 2-3 clamps per joint. I think that is very good :
From actual uses, at 180A charging/discharging, the off-the-shelf thick terminal lugs (#95) is a bit warm to the touch due to its limited copper contact area. Compare to what I use, hose clamps to wrap long strands of copper evenly onto the busrods, contact area can exceed 4-5X (~3") that of commercial lugs. They will never be bottlenecks or hotspots. But it is harder to install, more time consuming & not off-the-shelf. I personally trust this clamping method more than lugs, especially at high amps everyday, anytime, for decades to come. Bear in mind, it might not fit those who have local regulations to follow.
Picture of how I wrap my lithium spot welder probe working at ~1,800-2,000A. It is powerful enough to weld 0.20mm thick copper sheet.
