An ohmmeter should never be connected to which of the following?

An ohmmeter is designed to measure resistance in a circuit by sending a small amount of current through the component being tested. When it comes to a charged capacitor, connecting an ohmmeter directly to it can produce a potentially hazardous situation. A charged capacitor holds electrical energy, and if it's connected to an ohmmeter, the meter will attempt to measure resistance while the capacitor discharges through it. This can lead to inaccurate readings and could damage the ohmmeter or even create a risk of injury to the person using it due to the release of stored energy.

Before connecting an ohmmeter to a capacitor, it is crucial to ensure that the capacitor is completely discharged to prevent any unexpected voltage influences and provide a safe working environment. Thus, only after the capacitor has been discharged should it be safe to connect an ohmmeter to measure its resistance, confirming that option D is indeed the correct response.

In contrast, while it might be safe to connect an ohmmeter to a non-energized circuit or in specific testing conditions with a battery charger circuit, it is the charged capacitor scenario that presents the most significant hazard due to the inherent stored energy in the device.