"The maximum permissible current density of copper in open air is approximately 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively."
I came across the above statement when reading about copper in wikipedia.
Reference: - https://en.m.wikipedia.org/wiki/Copper
If the statement is true, a copper conductor with crossectional area of 1 square milimeter can only carry 3.1Amps of current in open air. If this rating is exceeded than the wire will heats up too much.
How true is this? How do cable manufacturers observe this limitation when designing cable and insulating the coppper with materials with poor thermal conductivity.? Within an insulation copper conductor will heats up much more faster.