Hi,
I have some old electrical books from the 30s or earlier and they often showed circuits with double pole fusing. I think the idea was that one fuse = good, two fuses = better. Therefore a fault would cause total isolation from the mains. Apparently, no one thought that one fuse might blow before t'other and the 50/50 possibility of the neutral fuse blowing first and thus rendering the faulty equipment still live!
I wonder how many fatalities it took before the penny finally dropped in later years and only the live conductor was then fused?
Cheers,
Pete