Quote Originally Posted by Desertboy View Post

Is there any point adding a slow fuse as well now I have working MCB type b protection?
I don't think so. The MCB should trip after a sustained overload, i.e. at something like twice the rated current, they should both trip within a minute (roughly). The B curve/C curve thing is about how much of a short-duration overload they can take to cope with switch-on surge and so on. That's not so different from a slow-blow fuse, so the only reason for fitting a fuse as well is in case the MCB doesn't work. How much should you trust safety devices? My machine has a couple of fuses on the PSU (commercial item) and one of those blew once. The PSU was operating well within its rating; it was just that the fuse was tired and didn't want to play any more. I'm not sure that I don't trust the MCB more than the fuse, but I don't have much experience of them in this kind of situation. On the other hand, all your house wiring is probably protected by a bunch of MCBs, so the people who make the rules trust them.