Originally Posted by rwidman
the ABYC requires circuit protection in all circuits except in the engine
I won't speak to what ABYC requires as this exception for fusing is aimed more at large motors but fusing a starting circuit on a sailboat is something that you should do. The small motors in sailboats do not require many amps to turn over and many boats are set up with banks that are used for both house loads and starting.
Here are a couple things to keep in mind. When you size wires you do so based on the round trip distance (e.g. a 15 foot run from the battery to the engine is sized as a 30 feet, 15 feet of positive wire and 15 feet of negative wire). When you size fuses, you do so based on the wire size, if it is located in the engine room and whether it is a single
run or a bundle of wires. If you reduce wire size as you branch off to other connections you need to add a fuse for the smaller wire. It is best practice to get the fuse within 7 inches of the battery; this might not always be possible but you should make all reasonable efforts.
The best resource I have found for sizing wire and fuses is this chart from Blue Sea Systems (warning it is a large pdf). http://assets.bluesea.com/files/reso...ence/20010.pdf
Another great resource for all things marine electric
is the Compass Marine
website. Compass Marine How To Articles Photo Gallery by Compass Marine How To at pbase.com
The owner of that website posts here as Maine
Sail. He also has his own forum section at sailboat owners. Musings With Maine Sail - SailboatOwners.com
For installing inverters specifically, most manufacturers I have seen require the inverter to be installed close to the batteries (typically under 6 feet) and specify the wire size. Based on the specified wire size you can get the fuse size from the Blue Sea Systems chart above. For instance, Xantrex PROwatt SW 2000 watt inverter recommends a 6 foot run of 0 AWG wire and a 250 A fuse. That agrees with the Blue Sea Systems chart for a single
wire inside of the engine room. Depending on your application this might vary.
Good luck and fair winds,