By far the most common application of thermal imaging/infrared thermography surveys is detecting “hot connections” in electrical installations
Any electrical connection oxidizes over time, increasing the electrical resistance of the connection and thus increasing the heat emitted by the connection when current flows through it. The heat in turn accelerates the oxidization process, which in turn increases the temperature of the connection – a vicious cycle.
This is totally invisible to the naked eye. A thermal imager can “see” this heat increase and enables the thermographer to identify future possible failures.