For equipment rated above 1000 volts the one MegOhm rule is usually stated as a minimum of one MegOhm per thousand volts. Although this rule is somewhat arbitrary, and may be criticised as lacking an engineering foundation, it has stood the test of a good many years of practical experience. It gives some assurance that equipment is not too wet or dirty and has saved many an unnecessary breakdown. More recent studies of the problem, however, have resulted in formulas for minimum values of insulation resistance that are based on the kind of insulating material used and the electrical and physical dimensions of the types of equipment under consideration.
For equipment rated above 1000 volts the one MegOhm rule is usually stated as a minimum of one MegOhm per thousand volts. Although this rule is somewhat arbitrary, and may be criticised as lacking an engineering foundation, it has stood the test of a good many years of practical experience. It gives some assurance that equipment is not too wet or dirty and has saved many an unnecessary breakdown. More recent studies of the problem, however, have resulted in formulas for minimum values of insulation resistance that are based on the kind of insulating material used and the electrical and physical dimensions of the types of equipment under consideration.
