So what is the current at which it will operate when continuously loaded under worst case scenario?
You have to check the tripping curve of the circuit breaker. Eg, Most circuit breakers installed in Australia are "C" curve. That is why you will see more than likely C32 indicated on the breaker. A 32A circuit breaker with 32A of current running through it is 1x its rated current, looking at the chart, at 64A, eg 2x rated current. it will take a whole 50 seconds approx to trip. At 33A, its going to take a VERY long time, hours, perhaps never if ambient temperatures are low. Common circuit breakers are thermal/magnetic, meaning that cant trip by heat generated by excess current (thermal) and magnetism generated by excess current. The point of the magnetic trip is that it doesn't have to wait for the bi-metallic strip to heat up before disconnection takes place. You can see in the chart that up to 5x rated current, its handled thermally, and after that, magnetically, Its a general requirement that circuit breakers disconnect a circuit with 0.4s at 7x the rated current for a C curve.
When installing a new circuit, you have to size cable to meet three main requirements (excluding physical factors):
- Current Carrying Capacity
- Voltage Drop
- Loop impedance to make sure the circuit breaker will operate within required time limits under fault conditions, eg the 7x rated current with 0.4s.
I wouldn't bother up rating all cable to allow for a C40 circuit breaker just because the maximum current is 32A on a C32 CB. If you were worried, you could set the wall charger to 31A in software. Rating everything for 40A would get expensive for no real gain.
You will also see another rating on circuit breakers like "3kA" or "6kA" etc. That is the maximum current that the circuit breaker can disconnected safely without welding it's contacts together. Again, something that the electrician should be checking. Although, its rare to see more than 1.5kA of prospective fault current in a residential installation.
