The fuse is to protect the wire. Sizing is not super critical when fusing for overload protection. You want a fuse that is equal to the wire's ampacity upto as much as 150% of the wire's ampacity. Here is a detailed explanation from Blue Seas at this link. Choosing Circuit Protection - Resources - Blue Sea Systems
07-14-2010 05:10 PM
Fuse size for a Yanmar 2GM20F
My new (to me) Seaward 25 has a Yanmar 2GM20F engine. I've read that its a good idea to protect the main power lines that go from the two battery banks to the battery switch by having a fuse at each battery. My boat is not wired this way.
I have seen fuses/posts that mount on the battery from Blue Seas, that look like they would do the trick. My question is: what size of a fuse do I need to protect wires, yet not blow when I am cranking the engine? I looked in the Yanmar manual, and the only info I could see was that it said the starter was "12volt; 1 KW". Does this mean I should be looking a fuse of around 100 amps, or it more complicated than that?