When measuring ballast resistance, what condition must the source be in?

When measuring ballast resistance, the source must be de-energized to ensure safety and accuracy. This condition is essential because measuring resistance while the circuit is energized can lead to inaccurate readings and poses a safety risk to the technician due to the presence of live electrical currents. When the ballast is de-energized, it allows for a safe and reliable measurement of the resistance without any interference from voltage.

In an energized state, there may be induced currents or voltages that can affect the measurement instruments, potentially leading to erroneous data. Similarly, measuring in a loaded condition could also introduce complexities related to the operational characteristics of the ballast, which further complicates accurate assessment. By ensuring the system is de-energized, you can confidently measure the resistance without these complications, thereby obtaining a clear understanding of the ballast's condition.