I don't believe the megohm scale or a DMM is will provide adequate voltage to test insulation values. Voltages from 100 to 1,000 are required to test insulation ratings up to 600 volts.
A typical rule of thumb for megging equipment below 1kV is one megohm. For equipment operating over 1kV, add one additional megohm per thousand volts of operating voltage.
Also, remember that megging helps establish a trend to determine the ongoig deterioration of insulation. Higher readings now, that are considerably lower in a year could help predict unexpected downtime. Conversely, somewhat lower readings that remain stable are probably a good indication.
[This message has been edited by Redsy (edited 02-04-2003).]
