The sadness I see on the faces of some students is almost too much to take sometimes.
For example, the looks I get in our Level I Thermographic Applications course, when we’ve just finished discussing how temperature measurements on bare metal is nearly impossible, and the room full of electrical folks just realized how much bare metal they will be inspecting. It gets kind of quiet. You can hear the shuffle of paper and breaking dreams. Just kidding, all is not lost! The most common discovery in electrical infrared inspections is the high-contact surface resistance anomaly. Abnormal resistance in a connection point causes abnormal heating, if you've spent much time inspecting electrical apparatus you've seen it. As discussed in Level I - Thermographic Applications, once that resistance has increased, the condition must be corrected for the abnormal heat to go away. Despite our assertion that temperature is but one consideration in assessing severity of findings, many people still ask the thermographer to quantify temperature as close as they can. The problem is that these connection points are usually bare metal components.
Luckily for us, usually right beside the spot where the electrical resistance has increased is a high emissivity spot. In low-voltage apparatus (anything below 1000VAC) insulated conductors are generally used (the exception being inside of switchgear). In an MCC, circuit breaker panel or control panel, the termination point where increased resistance has developed has insulated wire connected to it, and wire insulation is highly emissive. The insulation is less than an inch away from the connection point, so the thermal gradient is not large. Temperature measurement made there will be very close to the temperature of the point of high resistance. See the image below.
You’ll notice that there is a measurement point on the wire insulation closest to the termination point. This is a very reliable measurement due to the increased emissivity at this spot. When taking a measurement for comparison purposes, that measurement was also on the wire insulation for the same reason. The third measurement point is an attempt to determine the ambient temperature of the measured device, something we discussed in a different tip.
So, take heart electrical folk! Reliable temperature measurements are in fact possible for you if you continue to Think Thermally®.