I've got 32 years of doing and teaching forensic investigations. Your photos indicate the initial failure was likely within the shore charger, connecting the C1 cable from the main battery
switch to the ground wire. The most common cause would be failure of the charger transformer and here's why:
All but two wires/cables show external damage, not internal heat damage. Those two are the ground cable which is missing almost all insulation
, and the C1 cable. DC is fairly simple, in following internal damage toward the source of power. In your case, the closest the damage gets to a DC source is where the C1 cable attaches to the back of the battery switch, shown in this photo
Note that this is the point where the charger cable is a smaller diameter than the battery cable, probably 10 ga and 1 or 1/0 respectively. So here is the source of power feeding into the failure.
The reason a short to ground of the red C1 wire prior to arriving at the charger did not happen is because the damage would be limited to the C1 cable.
In this case, most of the length of the black ground cable has even more extensively internally heated to the point of nearly complete insulation loss. This more extensive heat validates what Jack C wrote, in that at some point current from more than just the C1 was carried by the ground cable.
The reason the red C2 cable from the battery switch is not showing evidence of internal heat damage is because the current from the C1 already would have heated the both the red C1 and the black ground cable and initiated thermal damage in both. (increasing heat increases electrical
resistance significantly) Therefore, by the time the C2 side of the charger circuit falilure developed inside the charger, the current through the red C2 cable was leading to where the C1 failure had already created a higher resistance path between the charger and ground. Therefore significantly less current went through the red C2 and you don't have the internal heat damage. (It will actually have damage if you section the wire, but you're going to replace it anyway so this is just academic.)
Within a charger is a transformer which typically has windings for both the C1 and C2 paths, plus the charger will have a rectifier for each. The transformer is where the C1 and C2 circuits come together, plus where they are closest to a path to ground. As discussed above, here is where the initial failure was the C1 circuit to the ground path, creating enough heat to then involve the C2 winding. A rectifier failure is an unlikely initial cause because it would need to be a double rectifier failure and that'd be low probability.
You could try to ask the charger manufacturer for a warranty replacement, but I'd suggest just swallowing the loss if they refuse and get on with life. Trying to go to court or somehow do anything further just isn't worth the cost.
So much for what happened. Note that power was not involving the MPPT
system so I wouldn't worry about electrical
damage to them.
When I teach forensic classes
, I tell students that wires are a lot like fresh brownies. Fresh brownies are soft and have all sorts of properties which interact just right with your taste buds. When wire is made the properties also hit a sweet spot in specifications regarding internal resistance, insulation resistance, thermal capability, etc. The problem with both brownies and wires is that damage is cumulative and never heals itself. If I put the brownies back in the oven
at a higher temperature or for a longer time at heat, they become hard or even burn, and it is the same for wires.
Obviously, the charger and cables need to be replaced completely and as so many other wrote, add fuses.
On installation of the new wires and cables, you've now had a great life-time lesson about why designers try to minimize chafe points and segregate:
and flammable sources from high current circuits. In boat
systems this generally means keeping the AC and anything heavier than about 14 AWG separated from flammables, especially not parallel above or below.
2. Critical circuits from non-critical. You can lose a battery charger, but would not want to lose the comm or all nav.
What I would further suggest at this point is to also replace any wire or cable that has any thermal damage to it because they became the over-baked brownies. (Note that thermal damage does not mean those only smoked or sooted. You'll know the difference because those can be cleaned.) Because there may've been high current shorts to co-bundled wires and cables, disconnect every ring terminal and connector related to those to look for blackening or darkened (overheated) insulation adjacent to the connectors and replace any that you find. Then test each of those for function of whatever is on the circuits.
Glad that you got away pretty easy.