I'll repost two in particular -
Notice how only the earth conductors are melted, and the active and neutral conductors are perfectly OK? This is what happens when you mix circuits of different voltages and don't put some thought into how you do it. I bet in this scenario the manufacturer has done three things - 1. used a chassis return for the negative back to the battery, 2. used piddly small cable for their connections to chassis and 3. has connected the 240V earth conductor to the chassis in multiple locations. What this does is create a situation where the 240V earthing conductor is a lower resistance path back to the battery than what the chassis is, so it ends up carrying all of the 12V DC current. 2.5mm
2 cable is only good for about 25A before it starts to melt, so it doesn't take many 12V appliances to draw that kind of current, so the earth conductor is overloaded and will melt. This is also the exact same reason why you always put the earth clamp close to the job when welding - otherwise electrical wiring ends up carrying welding current and will smoke away.
I notice in the post he goes to great lengths to say that the RCD or circuit breaker did not trip - of course it didn't, they aren't meant to detect faults of that nature.
This image is a perfect example of why you
always size your fuse or circuit breaker to the cable. The fuse/breaker should have activated long before this happened, but I bet it was oversized so it allowed this to happen.
