The question about sticking a 20a breaker on an overloaded 15a circuit got
me to wondering.

Last year I installed an invisible dog fence. The only outlet in the garage
already had an extension cord in it that ran to the garage door opener. So,
I ran #14 from the existing outlet (which I replaced with a GFCI) and put a
new outlet on the ceiling for the garage door opener.

When I was actually connecting up the wire, I realized the existing wire
#12; I checked the breaker and sure enough it was a 20a. I was fooled since
it was a 15a outlet, and code required a 20a outlet on a 20a circuit since
it was the only outlet on the circuit. (at least that is my understanding)
Since I didn't want to redo what I had already done, and I couldn't image
why I would ever need 20a on the circuit, I replaced the 20a breaker with a
15a.

Did I go to an unnecessary expense? Should I have just left the 20a
breaker? I can't think of a single situation where leaving the 20a breaker
would have been unsafe. Nothing but the garage door opener will ever plug
into the ceiling outlet (with the #14), and it is all exposed to the air, so
it is unlikely to overheat dangerously even if I did. Whatcha think?