The conductor question is actually legitimate. Copper bars can be a legitimate item. For instance nonfusible cutouts are just normal cutouts with copper bars installed instead of fuse links (typically SMU/DBU/CMU-20's). So as far as someone doing something illegal, that's not a good example. Different sizes for legitimate reasons also sometimes exists when the loads are single phase fed from a 3 phase system.

But yes different manufacturers and/or mixed types such as a Bussmann low peak fuse mixed with non-low peak fuses and occasionally different sizes is very common. As a motor shop engineer the biggest problem we run into is that no matter what is actually the problem, the call is always that there is something wrong with the motor. You get "this is the third motor we've put in and it keeps burning up, even after we bypassed the overload relay and put in the biggest fuses we had in the warehouse to keep it from tripping them. Your motors are junk." Wonder what happens if the maintenance workers keep burning up? Do they put in bigger ones to fix it?

Next week I'm doing fuses 101 for our sales people.

The fuses are all the same, but that's about the only thing correct in this switch...

Keep in mind, the fuse almost never provides overload protection. On a typical 2-5 second motor start (inrush) the optimal fuse size is 150% to 175% of the NEC table value when using time delay fuses, In other cases a non-delay fuse can be sized at 300% with NEC exceptions, as large as 400%. In affect, the fuse is only short circuit protection and sizing should have little impact on overload protection.

Flexible fuses?
This is a switch manufacturing error that no one caught. Do fuses maintain their rating when bent?

How would you feel about taking the fuse and brazing bus bars directly onto it and bolting it in rather than using fuse clips? Horrified? Well....

When performed correctly, soldering, silver soldering, or even brazing, should apply very little heat to the fuse elements.

In the photos above the fuse body on the left appeared a bit distorted.

To add further insult to injury, this disconnect, fused for 400-amps, was connected to 1000 amps of rectifer capacity. This system had two identical 400-amp fused disconnects, (the other disconnect didn't need bent fuses), connecting to separate 48VDC batteries on one side and a 1000 amp rectifier plant on the other side. After a battery discharge all the fuses will clear unless the DC load exceeds 200 amps.

I’m confused? It’s DC? If so not all fuses are tested for DC so there is always a selection problem. That might be the biggest TESTED size. Generally (RMS argument) the DC rating is about 50% of the name plate AC rating. Second sounds like redundancy if it’s not a max size issue by having two battery strings. A lot of utilities do it that way. If it’s all or nothing though then it is pointless. Often with DC fuses I see a lot of goofy, rare European brands with of course CE (not third party tested) marks.