For some reason I can't wrap my head around how inverse time overcurrent relays work.
Here are some trip currents and times from this curve for the Schneider Electric, Square D, QO 15A miniature circuit breaker (click image for larger size):
100 ms: 90 to 150 A
1.0 s: 67 to 120 A
10 s: 27 to 45 A
22.5 A: 25 to 125 s
30 A: 9 to 40 s
45 A: 2.7 to 12 s
Here is what I understand so far. If 90 to 150 A of current flows through the circuit for 100 ms than the circuit breaker will trip. If it flows for less than 100 ms and returns to normal current then the circuit breaker won't trip.
But if 90 to 150 A of current flow for 50 ms and then 67 to 120 A flow for 0.95 s and then 30 A for 30 s and then returns to normal current. When will the circuit breaker trip and why?
I feel like I'm missing some crucial piece information and that's the reason why I can't answer this simple question but I have no clue what it is.