Megging a DC motor

[Luketrician]

I've been doing some reading/studying this morning in a insulation resistance testing manual authored by Fluke.

It states in the manual, " when dc generators or motors are being tested the brushes should be raised so the coils can be tested seperately from the armature."

Is this the only reason why or will damage occur if the brushes are left on.

Or should I ask, is it possible to perform a safe and credible insulation resistance test on a dc motor without lifting the brushes?

 

[Besoeker]

I've been doing some reading/studying this morning in a insulation resistance testing manual authored by Fluke.

It states in the manual, " when dc generators or motors are being tested the brushes should be raised so the coils can be tested seperately from the armature."

Is this the only reason why or will damage occur if the brushes are left on.

Or should I ask, is it possible to perform a safe and credible insulation resistance test on a dc motor without lifting the brushes?

Unlikely to cause damage.
If there was a low reading, you might want to lift the brushes to find the source of the low reading.

To answer your second question, yes it is possible to get credible readings* - without lifting the brushes.
*For many, possibly most, industrial applications DC motors are shunt wound with the field and armature fed from different supplies electrically isolated from each other. For a complete test you need to check both.