It’s instructional here to note that the thermal test lab at the
PIC also included a thermal image test using thermography
similar to the field based IR scans. Fig. 13 shows the test lab
thermal image for Breaker 4919-1. Comparing this image to
the field IR scan shown in Fig. 11, the hot spot temperature
was recorded at 142.3oF, a value much lower than the
171.8oF hot spot temperature measured by the mill. This
suggests that perhaps some variable in the field such as an
unbalanced load or a line terminal that in fact was improperly
tightened, caused an overall higher hot spot temperature. It is
also interesting to compare the field and test lab overall
thermal images of this breaker. Note that the thermal profile of
the lab test appears more consistent throughout the MCCB