Yes, the cable I had going in there was 2.5 sq mm (only a short length, about 8"), and I had twisted it and folded it over. I'm well aware of the issue there, and yes, it was done up tight.
I noticed on one of the photos, it looks like the copper itself has oxidised in the connector - but was that cause, or effect? (of getting hot?!)
I just don't know what caused it. Its the first time I've ever had a failure like that and I've been doing this stuff now for 40 years.
As for fuses - main fuses to protect against catestrophic failure, sure. But they're some hundreds of amps - but then the battery leads are 35 sq mm too.
The PV arrays have protection.
I don't WANT to fuse between the rectifier and the batteries - if the fuse blows because of high turbine current - it means I've got a gale, and I don't want it running open circuit.
I've seen WAY more fuse failures over the years than I've seen these connectors fail, I guess what I was trying to say is to fellow RE folk, to keep your eyes open for anything that changes and investigate it.
(And do you REALLY think it's necessary to put a fuse in each and every wire that goes to each and every component - either side of every connector, and both ends of every cable "just in case"?? Sure, if we had infinite financial resources... or it was in a spacecraft...)