Testing with a Megger

[Bash1803]

Hi Guys,

I've been told a few different ways to do this by the blokes I work with.

Can anyone confirm to me though the correct and safe way to test single and three phase motors using a megger. Either balance testing (which I believe is using the ohms setting) or insulation testing (using the volts setting).

Many thanks in advance,

Bash

[HVACRsaurus]

To megger test a 3-phase motor with a 1000volt megger tester:

Testing to earth

a) Switch off the circuit breaker.

b) Connect black megger test probe to earth. Check for ground continuity, to a terminal box bolt (this is check for good ground connection)

c) With black probe still connected to ground, connect the red test probe to a motor terminal. Push test button. Insulation resistance should indicate 1 meg-ohm or more.

d) Repeat test on remaining motor terminals

Testing between windings

e) Disconnect all line connections & remove bridging links.

f) Identify the individual winings

g) Connect black probe to one winding, test with red probe to other windings. Again, insulation resistance should indicate 1 meg-ohm or more.

[install monkey]

g- ur only testing resistance so the reading will be in ohms- in 3 phase they should be equal in a single phase compressor they will be different according to start and run windings

[chemi-cool]

An important note, never ever megger a compressor when it is under vacuum!!

[RusBuka]

That can happen?

[install monkey]

http://www.youtube.com/watch?v=VBRG6AoEQIw&feature=share&list=TLzSbEhX7L1Nw

[nike123]

http://www.refrigeration-engineer.com/forums/showthread.php?11604-Compressor-insulation-measuring&highlight=fluke