I have a 4uf capacitor, working AC voltage 480v at 400 Hz and 600 VDC.
I'd like to know the working AC and DC voltage at 60 Hz.DC offset? If you may encounter DC offset you may consider keeping the peak voltage below 600 volts. That may result in a a greatly reduced maximum (reducing valve) allowable applied voltage.
It depends, if the voltage rating is dependent on the maximum voltage that may be applied to the capacitor DC offset may be a problem.
If the maximum voltage is limited by capacitor heating, (I am thinking of motor starting capacitors that will overheat if energized continuously at the rated voltage) then the capacitor may be able to withstand some DC offset.
Or, "AC and DC voltage at 60 Hz"  may be just misstated. grin ."AC with a DC offset". The peak voltage of  480VAC is 679V. The DC offset plus your peak sine voltage must be less than 679V. For good reliability the voltage needs to be a lot less than this. Some reliability specs require lower than 50%, some are OK with 90%.

MORE NEWS