Rik, you need to determine how much current the device at the end of the wire is pulling out of the wire. The fuse should be a little bigger, the most often next available larger size (e.g. current draw between 15 to 19 amps, therefore use 20 amp fuse). If there is more than one device connected to the circuit, add the loads of all the devices connected to / powered by that circuit (e.g. 7 light bulbs at say 1 amp each = 7 amps, therefore use a 10 amp fuse). Sometimes a device like an electric motor, will draw for a very short time a larger current at start up (inrush) than it does when steadily running; in this case a time delay fuse allows the extra start up current to pass without blowing, but will blow if the higher demand is continuous.
The wire should be sized according to the wiring chart to carry the load current you calculated, with a voltage drop acceptable for the devices powered (with too large a voltage drop lights will just go a little dim, but electronics might not work, the engine might not start or the batteries not charge).
In my thinking, it's better if the fuse capacity is lower than the wire capacity, and the load lower than the fuse capacity (but only a little) so that the cheap fuse is protecting both the wiring and
the equipment... my 2¢ worth
- hope it helps you!
"You start with an empty cup of experience and a full barrel of luck. The trick is to fill your cup before the barrel runs dry." - bljones