Don't Forget the Fuses
West has lots of good ideas, but only mentions the need for overvcurrent protection. Blue Sea has some good information on their site, including excepts from ABYC standards.The following was from my reply to Glenn Ashmore, in rec.boats.electronics, regarding unequal cable lenghts to 2 batteries. He had two 395 AHr banks, connected with 2/0 cable. Smaller systems will have smaller sizes, but the layout doesn't change.1. On the positive leads, you need to have overcurrent protection within 7"of the battery, or 72" only "If the conductor is connected directly to thebattery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box ...". This does not apply to starter conductors. (ABYC E-9)2. If your cable is rated 105 deg. C, the ampacity is 330 amps, outside theengine space (280 inside). 90 deg would be 285/233 (ABYC E-9). This is basedon continuous flow, which the National Electrical Code defines as 3 hours.3. I would agree with Peter Bennett, use independent leads and two switches.Each lead should have its own fuse. This provides separation and redundancy,for service and for faults.4. Fuses need to have 5,000 amps of interrupting rating(ABYC E-9), whichrequires ANL or class T fuses. The power released on a short circuit canexceed 50,000 watts. The fuses should be sized at the wire ampacity, theyare there to protect from short circuits. I would use class T, because they will carry 200% for 50 seconds, but clear 600% in about .01 seconds. 2/0cable would use 350 amp fuses.5. After the two batteries are combined, I would use thermal circuitbreakers for each individual sub-feeds: house panel, nav panel, winch, etc.I would use 3,000 AIC thermal breakers, like the Blue Sea 7000-7005 series.A 150 amp breaker will clear a 600 amp fault in .1 second, well before themelt time on the class T fuse. For the branch circuits, the magnetic tripbreakers are fine. Fuses are great for clearing faults, but breakers aremuch easier to reset.6. Ideally, your alternator regulator and charger should have a separatevoltage sense leads, both negative