From: J. Forster (jfor@quik.com)
Date: Thu Jun 02 2005 - 20:47:59 PDT
The purpose of the fuses is to protect the wiring in case of a circuit failure. As long as you fuse a circuit at or below the safe current carrying capacity of the wiring in that circuit under worst case conditions, you'll be pretty safe. Try a Google search on 'automotive wire current carrying capacity' Here are a couple of sites from such a search.
http://auto.howstuffworks.com/wfc1.htm
http://www.kampenwagen.co.uk/cable_tech.htm
There are also tables on the web of the current capacity (ampacity) of wires, given wire size and insulation types.
A couple of notes:
It is possible that a circuit may be fused at a lower value than the wire size may indicate, because the circuit may branch out somewhere. Headlights would be an example. You need to fuse for the smallest wire size in a circuit. (a chain is only as strong as it weakest link)
Next, connectors may have a lower current rating than the wire, if the system design is not perfect.
Finally, voltage breakdown is not much of an issue in 12 or 24 volt circuits. Insulation physical strength and oil and temperature resistance may well be of more importance.
FWIW,
-John
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