Originally Posted by janders
The manufacturer calls for a 135A breaker/fuse on the circuit but if I'm running parallel conductors of 1/0AWG and 4AWG, I don't really know how to size those fuses
Two good ways of doing this.
a) Protect both wires with a single
fuse, located upstream of the point where the wire "splits" and very close (inches; ABYC is quite specific for a reason) to the energy source (battery or a bus that is fed by a wire that is protected by something else). Rating of the fuse should be not greater than the ampacity of the lighter wire.
Only downside is that you cannot use much of the ampacity of the wires; in DC typically this is only an issue in very short runs where ampacity dominates. I would follow this route
for a windlass
b) Protect each wire with its own fuse, rated not greater than ampacity of the respective. This is not very "neat" in that you can think the circuit is not hot when it is (eg when you take one fuse out). We engineers do not like this option for a number of reasons but it is mentioned only for completeness. I would only do this if draw of the windlass
was greater than ampacity of the original (lighter) wire, which would be unusual on a "normal" boat.
Make sure you know where your drop comes form. IME windlass cables
tend to have quite a bit of drop from bad crimps that got corroded. You fix the crimp and solve the problem. I have found it useful to compare actual measured drop along the cable with the theoretical Ohm's law value (voltage drop = draw measured with clamp times resistance from a table that shows ohms per foot times length in feet).