Will a DC circuit breaker trip due to high voltage (exceeding voltage rating) or will it only trip because of high current? For example, if you have a 40 Amp DC circuit breaker which also has a 32 voltage rating would you have to keep the amperage below 40 and also keep the voltage below 32? Or do you only have to consider the amperage not going above 40?
Circuit breakers do not "know" the voltage of the circuit they are used in, so cannot trip based on that voltage - they only trip on over-current.
However, they are designed and rated to operate correctly (trip cleanly) only up to a certain voltage - using a 32 volt breaker on a 120 volt circuit may result in the breaker arcing when it trips (likewise, using a DC-rated breaker on an AC circuit, or vice versa, may result in faulty operation.)