Transformer Resistance Test

Resistance Test on a Transformer Connect an ohmmeter across the two ends of the primary winding of the transformer and record the resistance. See Figure.

Connect an ohmmeter across the two ends of the secondary winding of the transformer and record the resistance. See Figure.

Conclusion:

If an infinite resistance is obtained in either of the two tests this will indicate an open circuit in that winding and hence non-function of the transformer.

The resistance values of both windings may differ quite substantially due to the difference in the number of turns on each winding and also the difference in the cross sectional area of the wire in the primary and secondary windings.

To determine if the resistance values measured are correct, the manufacturer's specifications will have to be obtained and both resistance readings compared.