The choice of test voltage depends on whether a new motor (or coil) is being tested for
acceptance or whether an existing motor is being tested for continued service. Consult
your organizations’ policies regarding the HiPot test voltage to be used. The simple
formula of “2V+1000” generally results in a good test voltage for the HiPot test for
motors already in service. Other recommended HiPot test voltages can be found in IEEE
95, IEEE 43, ANSI C50.10-1977, IEC 34.1 and NEMA MG-1 (see chapter 2).
The HiPot test usually lasts one minute and the leakage current recorded at the end of the
minute. The leakage current at the end of this minute is to be recorded for future
comparisons. Between the time when the voltage is applied to the motor and the time
when the leakage current measurement is taken, the operator should carefully observe the
leakage current and watch for sporadically varying leakage current that might indicate
weak insulation. Such variations should be considered a failure of the insulation.