The arrester was put in to a salty fog in order to simulate the presence of a more severe pollution on its surface. Fig. 5 depicts a superficial discharge on the high voltage terminal of the arrester. This discharge probably is resultant from the presence of water drops the neighborhoods of the terminal. It can be observed in the thermal images that there is a greater heating in the proximities of the terminals and in the downer part of the arrester. As though there is a lower heating in its upper portion. The temperatures profile also indicates this situation. A possible explanation is that the pollution was concentrated in the downer region of the arrester, causing partial discharges there. Other possibility is the increase of superficial currents in the upper region of the arresters which would cause a lower leakage current to be conducted by the varistors. It is possible that at some point in the middle region of the housing, this superficial current decreases, as though the leakage current through the varistors increase. It would explain the larger heating in the downer part of the arrester instead of what is usually observed.