Comment by aix1

This sounded surprising and so I picked the first fuse I could find on RS and looked at its datasheet [1].

The characteristic curve shows that the 10A fuse is expected to blow after about 4s at 20A. Of course there's sample-to-sample variation and different ambient conditions etc, but how do those four seconds become "an hour to blow or not blow at all"?

[1] https://docs.rs-online.com/bc0e/0900766b81585c97.pdf