USA (California) home with 240V 150A service.
I have a contractor working on the house siding. He accidentally drilled though NM-B/Romex on a 15A circuit. (The repair of this is not my question and I will make sure that any splices will be in accessible junction boxes.) The the 15A breaker for this circuit is in a sub-panel, which is fed from a 240V 60A breaker in the main box. This, the breakers are effectively in series.
The interesting thing is that the 60A breaker tripped but, as far as I could tell, the 15A breaker did not. (I tried resetting the 15A breaker before I discovered the 60A was tripped; the 15A appeared not to be tripped but I know it isn't always obvious.)
My question is should I be concerned that the 15A breaker did not trip before the 60A breaker did? I realize that breakers should trip nearly instantly on a short circuit. Is it normal that the 60A could beat the 15A? (The 150A main did not trip.)
BTW, the sub was installed a few years ago by a licensed electrician, with permit and inspection. I'm certain the 60A breaker was new. The 15A breaker may have been moved from the main panel but if so, I'm pretty sure was installed a few years earlier in a remodel.