alsmith said:
When I looked for specific advice about ratings I couldn't find anything- it was all too vague. Like if you use 36V DC and want the fuse to blow at 60 Amps which 220V AC rating should you use? Which 110V AC rating should you use? The same rating for 110V as for 220V, or some set ratio difference?
What is the effect of using 72V DC instead of 36V- do you use the same AC rating or derate further, and by how much?
It seems to be a case of stick one in and if t doesn't blow then it's ok. BUT how much protection is it giving, is it giving protection that is actually of real practical value? It seems almost accepted that if it isn't blowing then the rating is ok- but that may just protect from a dead short. Or is that all they are being used for (in which case why not just use 100A, or 200A)?
I found this description for a breaker:
Interruttore magnetotermico ETA 1 polo, 250 V c.a./80 V c.c. 5A, 42mm
Means "250V AC/ 80V DC, 5A"
Link: http://it.rs-online.com/web/p/interruttori-magnatotermici/0333265/
Rs code: 333-265
But another says:
Interruttore magnetotermico ETA 1 polo, 250 V ca/50 V cc 10A, 29mm
Means 250V AC/ 50V DC
http://it.rs-online.com/web/p/interruttori-magnatotermici/4059286/
But both tolerate only small currents...
Another one:
Crouzet C4 Output Module w/ Fuse 100VDC/130VAC Output C4ORR5 USG
http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0.H0.X100vdc+fuse&_nkw=100vdc+fuse
It's hard to determine which is the correlation between AC and DC rating!
Anyway I also found a rare 80V-family of fuses (took weeks to find!):
http://uk.rs-online.com/web/p/automotive-fuses/2260866/
Most of so-shaped fuses are rated just 32V (I have a 60V scooter).
But these are permanent fuses.
, but just for ON/OFF and to fight shorts and reverse connections. Can not get B breakers, but it don't actually matter B is 3-5C only short trips it. If you use it on a bike, you will trip 40A breaker once a year o 60A current limit. Be safe! 
