When performing an infrared inspection of an electrical panel you may notice that the phenolic bodies of Ground Fault Circuit Interrupters appear warm. This same condition may also be observed on self-contained GFCI receptacles. This condition is usually due to the construction of the device itself. In order to monitor the amount of current flowing through the supply and neutral conductors of a circuit, GFCI devices have small transformers built into them. These transformers can cause the body of the GFCI to run several degrees warmer than ambient temperature. Depending upon the settings of your thermal imager, these device may show a marked contrast to their surroundings. 
When inspecting GFCI devices, compare the thermal patterns of these devices to other similar devices under similar load. When inspecting GFCI breakers, be sure to inspect the load side connection at the GFCI device as well as the neutral bus bar connection for the subject breaker. Infrared inspection of electrical distribution systems is one of the many topics covered in the Level I Infraspection Institute Certified Infrared Thermographer® training course.