During an effort to add an additional circuit my garage, I discovered that my house, which was built in 1999, has 14 AWG wire run off 20a breakers. My questions are simple:
Was this valid under code at the time of construction?
Do I have a problem that needs to be corrected?
I'm caught between trusting the circuits as they are, or biting the bullet and swapping all my breakers (about 20) for 15a. Not an insignificant cost or effort.
My background: I am a structures engineer. Basic electrical theory was covered as part of my education. I've been playing with electronics since I was a wee bairn. I recognized that this was insufficient to be play with electricity in the real world so I pulled up the 2016 NEC and drilled into relevant sections. After my fun quota was filled by that, I settled down with Wiring Simplified (44th ed.) to make it all make sense. With all that, I'm pretty confident that I understand residential wiring at a better-than-apprentice level.