What method would you use to check for an open primary winding in a transformer?

To check for an open primary winding in a transformer, measuring the resistance across the primary is a reliable method. This involves using an ohmmeter to assess the winding's resistance. An open primary winding will indicate infinite resistance, as there is a break in the circuit preventing current flow.

This method is effective because it allows the technician to determine the integrity of the winding without needing to apply power to the transformer. By ensuring that the winding has a specific resistance value that falls within the expected range, one can ascertain that the winding is intact. If the resistance reading is significantly higher than expected or appears as open, further inspection or replacement of the transformer would be required.

Other methods, while useful for different diagnostics, do not directly verify the condition of the winding in the same way. For instance, measuring voltage across the primary requires the transformer to be energized, which is not safe or appropriate when diagnosing an open winding. Inspecting physical connections may reveal loose or damaged wires but won’t confirm the winding's integrity itself. Using a continuity tester could be an alternative method, but it essentially accomplishes the same task as measuring resistance. However, resistance measurement provides a more detailed analysis of the winding condition.