# What is an acceptable power dissipation in automotive wiring?

I am trying to figure out what a reasonable power dissipation would be in a 12V automotive wiring harness to determine my wire gauges.

Is there any automotive standard that specifies what voltage drop/power dissipation is reasonable?

Regarding fusing, how much power can a wire dissipate safely before it starts to become a hazard?

Thermal dissipation under convective air varies from about 10 $$\W/(m^2K)\$$ in unenclosed still air to 100 $$\W/(m^2K)\$$ in forced air cooling. The area is the surface of the object in contact with air. Also keep in mind that hot air rises, so remember to orient fins (or attachment surfaces, e.g. automotive vertical vs horizontal metal chasis) appropriately.
Also, a common rule of thumb is to use 6 times wire cross section area (in $$\mm^2\$$) as continuous current carrying capacity (e.g. 1 $$\mm^2\$$ wire can continuously carry 6 A safely at 20 °C in open house wiring, and 4 A in conduit/junction box). Maximum/intermittent ratings can be almost double this. 4x cross section area is also used as maximum in transformer winding, where the traditional shellac coating had an absolute maximum limit of 120 °C.