What safety measure is necessary for working with electrical devices in wet conditions?

Using a ground fault interrupter (GFI) power supply is a critical safety measure when working with electrical devices in wet conditions. A GFI is designed to quickly cut off electrical power in the event of a fault, such as when moisture creates an electrical leak or when a person inadvertently comes into contact with a live conductor. This rapid response helps prevent electric shock, which can occur more easily in wet environments where water can facilitate the conduction of electricity.

While the other measures listed can enhance safety, they do not provide the same level of immediate protection against electrical hazards caused by moisture as a GFI does. For instance, wearing rubber gloves can help insulate against electricity, but if water is present, the gloves could still become conductive if water gets inside. Ensuring devices are weatherproof is also important, but it does not eliminate the risk of electric shock from a fault. Operating in pairs can be a good safety practice for various tasks, but it does not directly address the specific hazards posed by wet conditions and electrical devices. Thus, using a ground fault interrupter power supply is a necessary and highly effective safety measure in these scenarios.