Testing transformers

[mcelectrical]

Hi this is my first post on here> Can anyone help me with testing 12v transformers? I've tested low voltage bathroom fan transformers ok, but not low voltage light transformers. I'm using a Megger, and some of the transformers say 'dont test with a megger' on them? I guess i'm missing a trick somewhere?

 

[Marvo]

Are they wire-wound inductive transformers or electronic type? You should be able to 'Megger' them if you just use the 250volt testing range and not the 500/1000 volt settings.