...As cumbersome,and archaic as they are,I also concur with Joe regarding their reliability..The downside is...imagine a 42 circuit panel board filled with those things...Sheeesh!! At very least,a breaker design that would incorporate "fuse" technology wouldn't be a bad idea..There goes my Square"D" endorsement... Russ
.."if it ain't fixed,don't break it...call a Licensed Electrician"