With pointer multimeter and dry battery, the homonym terminal of transformer can be identified. The method is as follows: set the pointer multimeter at DC voltage 10V, connect it to both ends of the high voltage side winding of the transformer under test, connect the negative electrode of the dry battery to one end of the other winding, and contact the other end of the winding with the positive electrode. Observe the deflection direction of multimeter at the same time. For example, when the battery is turned on, the pointer is reversed, indicating that the winding end in contact with the positive electrode is in contact with the red meter of the multimeter. Be careful not to touch the transformer terminal during the test to prevent electric shock.

Power transformers should be polarity tested after handover and overhaul, and small transformers can be polarity tested as required.