Thank you! I've long wondered about this. Why is it then that the voltage is stamped on the fuse along with the amperage?
The voltage rating, in regards to a marine installation, applies to "AIC" or
amperage interrupt current for a safe trip. Let's say you have a bank that can throw 10,000A of short circuit current (eg: two G-31 Odyssey AGM's), then you'll need a fuse that can handle 10,000A of short circuit so it can trip and so safely on your 12V system. The AIC current rating should never be confused with the trip current. Eg: a 300A fuse would need to be Class T if the bank has the capability of creating 20,000A of short circuit current. AIC is all about the over-current device not failing when trying to do its job.
As the fuses voltage rating goes up the AIC rating goes down. For example the very common MRBF fuse is AIC rated for a 10,000A safe trip at 14V but only 5000A, or half, at 32V.
Standard Marine Fuses & Their AIC Ratings:
*Class T = 20,000A AIC @ 125V - (Significantly higher at 12V) (*Class T Complies with ABYC for LiFePO4 batteries)
MRBF = 10,000A AIC @ 14.0V
ANL = 6000A AIC @ 32V (Higher at 12V)
We've seen a fair number of circuit breakers literally welded shut because the AIC rating was not considered when choosing the over-current protection for the bank. We've also seen un-safe failures of ANL fuses when the AIC rating was not applied correctly.