For equipment that has been in service, the test voltage may depend upon the type and condition of insulation,
equipment history, desired service reliability, etc. In general, an alternating voltage test ranging from
125 to 150 percent of the rated rms line-to-line voltage (E) has proven adequate. This is approximately equal
to 65 to 75 percent of 2E + 1000 V, depending on the voltage rating of the equipment to be tested. The directvoltage
test value for maintenance tests is 1.7 times the alternating voltage (rms) maintenance test value (50
Hz or 60 Hz).