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I'm adding a Blue Sea dual battery switch to a Yanmar diesel setup.
Don Casey,in Sailboat Electrics Simplified advises adding a fuse near the battery on the charging wire to prevent fire.
However, the engine on this boat has only one red cable coming from the engine compartment which is connected at the the starter. Then (via a short jumper) connects to the alternator B+ terminal.
Installing a 60 amp fuse in this line (alternator is 55A) results in instant blown fuse when starter engages.
My thought is to separate the alternator from the starter (by removing the jumper) and add a new run from the alt to the fuse mounted on the common post on the new switch. The remaining starter wire could be installed under the fuse holder on the same post creating a direct connection to the starter from the battery switch but routing the charging current through the fuse to protect the wire.
Or should I just resize the fuse to handle the starter load?
 

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The fuse should be sized to handle the starter load, since that cable is a starter cable, as well as the alternator output.

However, if you want to make the alternator idiot-proof, and protect it from human stupidity, it would be wise to wire the alternator, with a fuse, directly to the house battery and remove the short jumper. This would prevent the alternator from frying itself if anyone puts the battery switch into the off position by accident.
 
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