Minimum values of insulation resistance

mapj1:

Round numbers like 1 million have the feel of some one trying to make a good stab at an order of magnitude.

Zoomup:

Why was one MegOhm chosen?


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.


Z.

Wombat:

Zoomup:

Why was one MegOhm chosen?


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.


Z.

Can you provide any references to these studies for XLPE and PVC insulated cables please?

 

Harry Macdonald:

However, if you do get 1Mohm on a new, clean, dry bit of wiring it is probably a good idea to investigate why before saying "OK, it passes". But is it is on a circuit with several old motors and contactors then no need to investigate further.