Hi,
I purchased a transformer in an auction recently. But I am not sure whether it is really an isolation transformer. What tests could be carried out to determine that it is an isolation transformer and not an autotransfomer ? Can anyone help? Thanks.

 

The autotransformer has 3 pins. The isolation transformer has 4 pins

 

Both primary & secondary windings of the isolation transformer will have the same DC resistance as measured with a multimeter.