What condition does reading 0 ohms at the secondary winding of a step-down transformer indicate?

Reading 0 ohms at the secondary winding of a step-down transformer indicates a shorted secondary wiring. In a properly functioning transformer, you would expect to see a certain level of resistance, which reflects the integrity of the winding. A reading of 0 ohms suggests that there is an unintended connection within the secondary winding, effectively shorting it out. This situation could lead to excessive current flow, which may damage the transformer and disrupt the electrical system it's a part of.

In contrast, normal operation would show a measurable resistance, indicating that the winding is intact. A disconnected primary winding would not even provide a resistance reading, as there would be no continuity in the circuit. Excessive voltage present does not directly correlate with the ohmic reading but would rather be identified through voltage measurement rather than resistance. Therefore, the 0 ohm reading signals a significant issue requiring immediate attention.