Fuse Sizing

[redsky49]

In the illustration on the right, if both resistive loads are energized simultaneously the breaker will trip, opening the circuit (in most cases).

It is unclear to me what the author is trying to illustrate here. I simply don't know.

Mr. Casey has written for years for BoatUS, Sail magazine, International Marine, etc. Despite this, I am unable to locate any direct contact information, so we may never know what the author intended.

For the right side illustration, you could, per AYBC, provide a 60 amp breaker, and maybe not have nuisance trips (though I doubt it), or rethink the wire gauge to #8, along with a breaker/fuse at 70 amps and be protected (as well as having lower voltage drop). I would choose the latter.

[john61ct]

Originally Posted by masonc

The breaker size is determined by the cable, not the load. The cable is determined by the load.

No, as has been clarified many times above, if you plan a circuit to carry maximum X amps, but decide to use a heavier cable than what safety requires to reduce voltage drop, then it would make sense to size CP (and buss, connectors etc) to the smaller load rating.

[boatbod]

Originally Posted by john61ct

No, as has been clarified many times above, if you plan a circuit to carry maximum X amps, but decide to use a heavier cable than what safety requires to reduce voltage drop, then it would make sense to size CP (and buss, connectors etc) to the smaller load rating.

Well the standards only quantify the maximum size circuit protection that can be employed for a given wire size/ampacity. Obviously you can decrease the breaker size if you aren't going to carry as much current.