If the megger indicated greater than 100M ohms your insulation is OK.
In a nutshell if a megger reads open like above, the test passed. If you get a reading the test failed.
A megger is simular to a ohm meter on a DVM, but it uses a AC voltage at 50 volts or higher. This gives it the ability to punch through pin holes or arc tracts. So what you are looking for is any type of a reading.
The old hand crank ones are great for driving worms out of the ground.
