Which of the following is NOT considered a type of overprotection?

A flow switch is not considered a type of overprotection because its primary function is to monitor the flow of a fluid within a system and to provide an indication of flow conditions. This device can help ensure that the system operates efficiently and can prevent issues related to inadequate flow, but it does not serve a direct protective purpose in scenarios where overpressure occurs.

In contrast, pressure relief valves, rupture discs, and fusible plugs are all safety devices designed to protect a system from excessive pressure. Pressure relief valves automatically open to allow fluid to escape when pressure exceeds a predetermined threshold. Rupture discs provide a one-time failure point that creates an opening to relieve pressure, while fusible plugs will melt at elevated temperatures, releasing pressure and preventing potential hazards. These devices are all critical for maintaining safety in refrigeration and other pressurized systems, which is why they are categorized as forms of overprotection.