For many years, maintenance professionals have used the one-megohm rule to establish the allowable lower limit for insulation resistance. The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm.
In contrast, testing with AC gives a charging current that is extremely large compared to the other kinds; leakage current is relatively minor. AC frequently is used for highpotential testing; voltage is increased to some specified point to see if the insulation can stand that particular voltage. It is a GO/NO-GO type of test and can cause deterioration of the insulation, in contrast to the DC test which is basically non-destructive. If an AC test voltage has been used and you want to use DC tests as an alternative, you will need to increase the maximum DC test voltage somewhat to obtain equivalent results.
For many years, maintenance professionals have used the one-megohm rule to establish the allowable lower limit for insulation resistance. The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm.
In contrast, testing with AC gives a charging current that is extremely large compared to the other kinds; leakage current is relatively minor. AC frequently is used for highpotential testing; voltage is increased to some specified point to see if the insulation can stand that particular voltage. It is a GO/NO-GO type of test and can cause deterioration of the insulation, in contrast to the DC test which is basically non-destructive. If an AC test voltage has been used and you want to use DC tests as an alternative, you will need to increase the maximum DC test voltage somewhat to obtain equivalent results.
