The main nominal characteristics should be marked close to each item of
equipment. For example, for power transformers, the voltage ratio, power rating
and vector group should be provided; for power circuit breakers, the nominal and
short-circuit current ratings; the transformation ratios for voltage and current
transformers, and the nominal voltage of lightning arresters. Voltage transformer
circuits should be drawn physically separated from the rest of the circuits, and the
connections to the coils of the instruments that require a voltage signal should also
be indicated. As a minimum, the AC diagram of a transformer should include all
the equipment in the bay between the high voltage busbar and the secondary
bushings of the transformer.