Yes there was a red flag moment but think about it, it worked fine, its probably worked fine since the 50's, yes the house had had a fire but it didn't get to the mains cupboard, the old plastic CU was still intact. So what could cause a 80A fuse to blow in the middle of the night with no-one around and absolutely no load on it, its not like the cut out has moving parts that had failed.Yes. I've taken out a supplier fuse when an entire installation was reverse polarity, and certainly mistakes were made leading up to this, but I learned from it.
I get that you left things working one evening, and the next morning for no apparent reason everything was dead.
Red flag number 1 was obviously that supplier fuse had blown. That would immediately make me think something very significant has happened.
Red flag number 2 was that the RCD and MCB were still in the ON position. So the cause must be upstream of them. This would put me in "something exceptionally unique and wacky has happened" mode and caution levels would rise to paranoid levels.
The absolute last thing I'd do is bung another fuse straight in and 'see what happened'. Continuity/IR testing at your incomer on your CU would be where my mind when next.
As for creating your own low value fuse, still without having any idea what caused the fault or finding a way to measure it, well I'm honestly rather stunned.
Out of interest, what was causing the short, the end of the tails, or the terminal itself?
Was the cut-out safe for continued use afterwards?
My conclusion to the red flag moment was it has to be a faulty fuse, so I replaced it. As for the very thin fuse wire trial, I thought that was quite a good idea, couldn't have been more than an amps worth of wire, I disconnected everything, even the tail out of the top of the fuse holder and it still went with a bang but with a lot less sparks and arcing this time.
s for the problem, I have no idea, I still cant fathom what went wrong, I got the office to call the DNO out and I wrote on the cut out "do not energise" By the time I came back to second fix it had a brand new head on it.
I still don't get all the hoo-ha about it though, it seems some people are ---- scarred of a big bang, you see it when someone is going to cut a cable which might be live with insulated snips, try as they might, they just can't bring themselves to do it even though they know they are perfectly safe from injury, its the bang you see.