On another post I expressed concern about the idea of changing a breaker size without knowledge of the wire size used in the circuit. There was a reference to an outside article that talked about how much current a given wire size was capable of handling. The article was not well researched and I volunteered to get the facts.
First some philosophy about sizing breakers. I spent most of my career in engineering and manufacturing as an OEM supplier. That is someone who supplies equipment for installation in someone elses vehicle. I believe. equipment should be designed to contain its own problems. That is it should not fail if supplied adequate power. Moreover, no failure should cause failures in the parent vehicle or any other equipment.
Second, Breakers should be sized to protect the wire. Wire current carrying capability depends on how the wire is routed and how long the current lasts. That is, for short times the wire can carry extra load with out failing. For long lengths of wire the voltage can drop over the length of the wire due to inherent resistance in the wire.
The US Department of Commerce publishes a nomograph for selecting proper copper wire sizes depending on current load, wire length and application. I used this nomograph to develop the following table. The table is limited to typical current loads we will find in RV applications. I used 20 feet as a typical length and made sure we were not going to see any voltaage drop. There are three applcations cited. Continuous load for bundled wire, continuous load for free standing single strands of wire and for intermittent load of two minutes maximum.
To use the chart, determine the current load and then select the column for the application. The cell at the intersection contains the MINIMUM wire size.
The table can be used bacwards: if you know wire size you can determine how many amps can be carried.
This table is for copper wire, either solid or stranded, in 12 volt (13.6 volt battery)applications