Preinstallation Test. All instrument transformers used for billing purposes shall conform to the requirements of Regulation .03E of this chapter before being placed in service. Current Transformers. Current transformers should be tested with a suitable variable burden device to determine if the windings of the secondary circuit have developed an open circuit, short circuit, or unwanted grounds. Potential Transformers. Potential transformers should be tested by measuring the secondary voltage to reveal defects in the transformer or secondary circuit which appreciably affect accuracies. Performance Test. If there is any evidence that an instrument transformer is inaccurate or has been damaged to the extent that its performance has been impaired, it shall be tested to determine whether it should be replaced.