I'm wiring an electric kiln that consumes 43 amps. Since it's a continuous load device, I understand that the wiring needs to be capable of handling 125% of that load, which is 53.75 amps.
I have a 25ft length of 6/3 NM-B (https://www.amazon.com/Wirenco-Non-Metallic-Sheathed-Residential-Equivalent/dp/B08R6LQGGR/) whose allowable ampacity is 55 amps.
There are no 55 amp breakers, but I've read that for applications under 800 amps, one can use the next largest standard size breaker - in this case 60 amps.
I'm clearly not an electrician (and am trying to learn so please don't ream me out for asking).
Is my understanding correct?
If so, why is an upsized breaker safe in this scenario? It seems like if there were a continuous load of 59 amps it would not trip the breaker but would exceed the capacity of the wiring. How is that okay?