I have a tandem circuit breaker in my main breaker box with two 20 amp breakers. To turn off power my wife's office, I need to throw both breakers. I can throw either one and as long as the other is on, the circuit is still live.
My guess is the electrician who installed this tandem breaker wired it in parallel. In other words, current is flowing through both breakers when closed and both have to be open for it to break the circuit. Does that sound right?
If so, my understanding is that it would take 40 amps of current to flow before this breaker would trip. (20 amps X 2 = 40 amps because it's in parallel)
They used 12 AWG wire on the circuit. That means the wire would basically catch fire before the circuit would actually break. This seems incredibly dangerous.
Are my assumptions correct in this case? I'd like to know so I can get a electrician out to inspect the wiring, since I've spotted a few other oddities in this house.