The discovery that accurate temperature measurements are many times difficult in electrical applications of thermography can be a hard pill to swallow. Electrical apparatus are often made from metal that’s bare, so emissivity is low, and thus temperature measurements are unreliable.
The good news is that despite this fact, electrical anomalies can be relatively easy to detect, but only if you know what you’re looking for. The simple fact is that electrical circuits with current flowing through them will inherently generate heat. It’s a byproduct of normal operation. So when you inspect electrical apparatus, guess what? It’s often hot. The important thing to determine is what kind of hot is it?
What do we mean by that? It’s the pattern that’s important in the discovery of electrical system anomalies. The lion’s share of abnormal heating in electrical system components is abnormal electrical resistance on a contact surface. We discourage thermographers from saying “loose connections” because in truth there are many other causes for increased resistance, and in many cases the connection is plenty tight. Something else could be amiss. Take a look at the image below.
Notice the pattern. The area of the highest thermal energy is at the connection point, and the circuit gets cooler the further away from the contact point. This thermal signature is most often associated with increased surface resistance at the contact surface. The greatest amount of heat is generated at the point of resistance and then it conducts away from its point or origin, resulting in the telltale “trailing away” pattern.
So remember, in electrical applications it’s not usually a matter of how hot a thermal anomaly is, it’s what kind of hot it is.
Think Thermally, www.thesnellgroup.com The Snell Group, a Fluke Thermal Imaging Blog content partner