In addition the positive bus in the picture isn't covered.
I have seen inverters fail when one of the 2 DC leads melted while the other looked perfect - not that rare at all. In one case I was hired to replace a dead inverter
- 2000 watt Freedom - and the first thing I noticed was cabling way too small, 1 or 2 gauge for a long run. After convincing the owner to replace the cables
("But it was professionally installed"
) we removed the old cables to get their length. The positive wire was near perfect but the last few feet of the negative at the battery
end was bare as the cover had melted off and the wire here was stiff and corroded. We went with 3/0 for new cables.
I attended an inverter
fire once as well.
The wire with the most resistance will get the hottest and in a marginal situation of too small cabling and/or too long a wire run it may not happen when new but after a while, sometimes years it certainly can.
If Xantrex states 6' as a maximum abide by it. With the 13' x 2 run my calculator comes up with 2/0 for a 2% drop so with your overlong run 2 gauge was way too small.