If you can load a 15a breaker/14ga copper circuit enought to warm the
wire you have a defective breaker.

Breakers are NEVER defective? That's good to know! Thanks!!!

If you have a defective breaker it doesn't matter how big your wire is.
Available fault current in a home is in the thousands of amps. (only limited by
the size of the service drop)
That was not the discussion.