When testing a transformer, what does a reading of "open" indicate?

A reading of "open" when testing a transformer indicates that there is an interruption in the circuit, meaning that the transformer is not operational. When a transformer is functioning correctly, it should present a closed or low-resistance circuit. The open reading suggests that one or more components within the transformer are not allowing current to flow, which points to a fault in the transformer. This could be due to issues such as a break in the windings, a failed insulation, or other internal problems that compromise the transformer's functionality.

In contrast, the other options imply operational status or new condition, which would not be indicated by an open reading. Thus, the presence of an open circuit is a clear sign that the transformer is faulty and requires further investigation or replacement.