The working voltage of a capacitor in an AC circuit should be __________.

The working voltage of a capacitor in an AC circuit should be __________.

• A. Equal to the highest applied voltage
• B. Slightly less than the lowest rated voltage
• C. Twice the highest applied voltage
• D. At least 50 percent greater than the highest applied voltage

Answer: (D)

In AC, the voltage across a capacitor swings with time, so the critical value is the peak voltage—the highest instantaneous voltage the capacitor must withstand. The working voltage should be chosen with enough headroom above that peak to tolerate tolerances, temperature effects, aging, and possible transients. That’s why a margin of at least 50 percent greater than the highest applied voltage is a sensible rule of thumb: it ensures the capacitor won’t approach its dielectric limit during normal operation or surges. If you matched the rating exactly to the peak, there would be little to no margin for variations; lining up a rating well above the peak avoids stress and potential failure. The other options either provide no margin or are unnecessarily conservative for regular design needs. When applying this to AC, remember to compare the rating to the peak value (not just the RMS), since the peak voltage is the one that drives dielectric breakdown.

In AC, the voltage across a capacitor swings with time, so the critical value is the peak voltage—the highest instantaneous voltage the capacitor must withstand. The working voltage should be chosen with enough headroom above that peak to tolerate tolerances, temperature effects, aging, and possible transients. That’s why a margin of at least 50 percent greater than the highest applied voltage is a sensible rule of thumb: it ensures the capacitor won’t approach its dielectric limit during normal operation or surges. If you matched the rating exactly to the peak, there would be little to no margin for variations; lining up a rating well above the peak avoids stress and potential failure. The other options either provide no margin or are unnecessarily conservative for regular design needs. When applying this to AC, remember to compare the rating to the peak value (not just the RMS), since the peak voltage is the one that drives dielectric breakdown.