AC is typically quoted as the AC RMS Voltage. E.g. UK mains voltage of 230V AC is 230V RMS.
Peek AC Voltage
Calculating the peek voltage of an AC RMS voltage: VAC * sqrt (2)
Example: 230 V AC RMS * sqrt (2) = 325 V peek
Example: 1500 V AC RMS * sqrt (2) = 2121 V peek
Testing insulation with AC or DC voltage
Insulation breakdown tests
Where insulation breakdown is concerned you are always interested in the maximum voltage possible. So the equivalent DC voltage to AC is the peek AC (e.g. 1500V AC RMS or 2121 V DC)
– or we could test to dc equal to peak AC voltage which would be 1500 * sqrt (2) = 2121V dc.