Lately I have had a number of questions about battery bank fuse sizing and I wanted to give a brief explanation of how I size these fuses and why they are a good safety feature..
*Simply put you size the fuse to protect the wire, provided your wire is sufficiently sized.
The ABYC Standards On Bank Fusing:
The ABYC requirement is for a battery bank fuse to be within 7 wire inches of the battery bank. In the real world of boats and battery compartments this is often hard to do. If you can't get within 7" then the next best thing is to be as close as possible but the wire should ideally be in a protective sheath or conduit.
If you're having trouble meeting the 7" rule, the Blue Sea battery terminal fuses shown in this photo are an excellent option. These fuses are excellent but they do add nearly 2", in height, to a battery post so measure your battery compartment height carefully.
The limiting factor with the battery terminal fuses is that they only go to 300A so if trying to fuse a bigger engine you may need a Class T or ANL fuse.
If you prefer to cut to the chase I will give you the bottom line minimum bank fusing I like to see for any bank that could ever be called upon to start a motor:
Minimum fuse size for small sailboat diesel AUX engines 8HP to 35HP = 250A
Minimum fuse size for medium sailboat diesel AUX engines 35HP to 60HP = 300A
Above 60HP 80% of in-rush as minimum fuse size.
If you follow these guidelines you will not suffer "nuisance trips".
As a service to my readers I offer the Blue Sea battery terminal fuses, shown above, in the MarineHowTo.com web store, and at very competitive prices. Purchasing products through MarineHowTo.com keeps the site running and helps to keep it FREE! The Blue Sea fuses are sold as a package, fuse & holder together for just $29.95. My prices beat Defender, West Marine and just about anyone out there selling the Blue Sea fuses.
Purchase a Battery Terminal Fuse & Holder (LINK)