A monitor can sense the difference in temperature between the inside and the outside of an enclosure containing electrical power equipment. The monitor has a case adapted for mounting at the enclosure. Also included is a first and a second sensor for producing a first signal and a second signal, respectively. The first sensor is mounted at the case and is adapted for insertion through an opening in the enclosure. The second sensor is adapted to sense temperature at a location remote from the first sensor. Specifically, the case is mounted so that one of the sensors is inside the enclosure and the other is outside. The monitor also includes an alarm system mounted at the case and coupled to the first and the second sensor for producing a warning signal in response to the first and the second signals from the first and the second sensor signifying a temperature difference exceeding a predetermined threshold.