What action should be taken to ensure that a rectifier is safe to touch?

To ensure that a rectifier is safe to touch, measuring the case-to-ground voltage is critical. This action helps determine whether the rectifier's case has any unintended voltage present that could pose a shock hazard. If the case is energized, it indicates a fault that needs to be addressed. By measuring the voltage between the case of the rectifier and ground, an operator can make an informed decision about the safety of the installation before performing any maintenance or inspection.

While checking the current output or the fuse status might provide insights into the functionality of the rectifier, they do not directly assess electrical safety as it pertains to potential shock hazards. Grounding the rectifier is also a necessary safety measure, but it should be done correctly and verified first—this is typically part of ensuring safety rather than a defining check. Measuring the case-to-ground voltage directly identifies immediate hazards, making it the most effective action for verifying safety before touching the device.