MRBF Fuse Required

[Nichole340]

I’ve been reading your ”New Articles” this morning. Thank you so much, I’m praying for your recovery and rehabilitation.
The Battery Over-Current protection is of particular interest to me.
I have 2/0 AWG Battery cables from Start Battery to starter. About 10 feet long. With 3 Group 31 Wet Cell, 12 V, 130 A/hrs. 2 as House Bank and 1 as Start Bank.
I know I’m protecting the wires, so Just to clarify if I am reading the Blue Seas chart correctly, I need a 300 A fuse, on my Terminal Block Holders on the battery.
I want to make sure I’m not doing this wrong.

Thank you.

 

[kappykaplan]

I'm tagging @Maine Sail for you.

 

[Charlie98117]

Mainsail has an excellent article on this, Battery Banks & Over Current Protection - Marine How To . He notes a fuse on the start circuit is not required by ABYC standards but recommended despite the potential for a nuisance trip. There is a paragraph that recommends min 300 amp for engines up to 60 hp so I think you're OK with your selection and considering you have a 27 hp Yanmar 3GM30F in your H340.

 

[Nichole340]

That’s what I have, 3GM30F. I just wanted to confirm my installing a 300 A Fuse. Thank you all.

 

[Scott T-Bird]

@Nichole340 yes, you are interpreting the chart correctly. By way of explanation, you are basically allowed a 300 amp fuse if you have a single cable that isn't bundled with a other cables. The chart is recommending lesser amp fuses for cables that are bundled. The reason for this is to provide greater protection for cables that may suffer greater heat when bundled. As you noted, the fuse is for the wire's protection. The smaller the fuse, the greater the protection and vice-versa. When you are reading Maine Sails articles, he does explain that the starting circuit is only momentary, therefore, it is relatively safe to use larger fuses to prevent nuisance breaks. With a fuse, a break requires a new fuse, obviously, so breaks are expensive!

But, to end a long story, you should be perfectly fine with 300 Amp fuse. That's what I use with my 1/0 cables. In fact, I've had a 225 amp fuse for 2 seasons (same engine as yours) and never a break.