If that is in fact a backfed main breaker, it should have a means for holding it in place (screw, rivet, bracket, etc) so it doesn't just pull off the bus, or it's a violation. Sorry, no Code book today, so I can't give a reference.
Randy, what's the 3rd pic? Is that a flex connector with something slid over it like EMT or maybe a white garden hose??...S
