Hot Spot Detection—What to Look For

If you don’t know what to look for while carrying out infrared testing of electrical equipment using a thermal camera, things can get complicated. First, it’s important to know that temperature measurements can’t be relied upon. Why’s that? It’s because the emissivity is low in electrical components as they are primarily of bare metal.

How well a material emits infrared energy compared to a perfect radiator is referred to as its Emissivity ratio. Emissivity values are always within 0.0 and 1.0, and any object with an emissivity ratio reading of 1.0 is considered a perfect radiator and called a “black body.” Note that no radiator reading is ever actually perfect.

Due to this complication, it is difficult to carry out quantitative inspections to obtain accurate temperature measurements using infrared technology. This is why many thermographers opt to conduct qualitative inspections where the focus is on recording the apparent difference in temperatures between comparable equipment made to operate under comparable loads. Another approach is to operate the same equipment under comparable loads over a certain period.

Here’s a simple example- take the image of a hand with a key on it. While the key and the hand are at a similar temperature, there will still be a difference in the thermal image, with the key appearing colder than the hand. This is because while the hand and the key are at the same temperature, the amounts of infrared energy radiated by them are different.

Despite this scenario, if you know what to look for, it can be pretty easy to detect electrical anomalies. Heat being a byproduct of regular operation is a simple fact. Heat is generated when power flows through electrical circuits. That’s why electrical components are often hot when they are being tested. You have to judge whether this heat is caused by normal or abnormal heating.

It’s crucial to study the thermal pattern when detecting anomalies in electrical systems. In a vast majority of cases, it’s the abnormal electrical resistance on a contact surface that triggers abnormal heating in the electrical system components.

The rise in resistance may be caused by,

  • Phase on short
  • Winding to winding resistance imbalance
  • Breakdown in insulation

In thermal images of hot spots, you’ll notice the area with the highest thermal energy located at the connection points. This is because the circuit gets cooler the farther you’re away from the connection points. The increase in surface resistance at the contact surface is what this thermal signature is associated with most often. The “trailing away” pattern results from the greatest heat being generated at the resistance point, which reduces as you move away from the point of origin.

Understanding Thermal Images’ Emissivity

Temperature, spectral wavelength, surface condition, and viewing angle are the factors that decide variations in emissivity. Energy radiation occurs efficiently in most non-metallic materials. With an emissivity reading of 0.98, human skin is closest to being a perfect radiator. With an emissivity value of 0.01, a polished copper surface comes at the other end of the spectrum.

The emissivity setting can be changed in most infrared cameras. Therefore, you can make adjustments in the camera that’ll allow you to get close to the actual surface temperature, provided you’re aware of the emissivity value of the material being inspected. However, you can’t obtain an accurate temperature reading using infrared cameras if the material has an emissivity of less than 0.60. In addition, the temperature reading you get with an infrared camera may still not be accurate even if the emissivity is above 0.60, as the temperature reading may be affected by other factors.

Having discussed what you should look for during hot spot detections, let’s get to know more about infrared cameras.

What can thermal cameras detect? 

You can measure heat detected with a thermal camera very precisely. This allows for its multiple applications. For example, you can detect even the minutest difference in the heat with an infrared camera- even if it’s just 0.01°C. It can then be displayed in shades of grey or various colors.

Thermal energy is emitted by every object we come across in our daily lives, including ice. The thermal energy of an object is more if it’s hotter. The thermal energy an object emits is called its “heat signature.” Irrespective of the lighting conditions, when there’s even the slightest difference in heat signatures between objects, it shows clearly in a thermal sensor. This allows infrared cameras to be able to see in complete darkness or even when things are hidden by smoke.

What do We Use Thermal Cameras for? 

Infrared cameras convert temperature differences after detecting infrared energy into visual images. There’s no end to what infrared cameras can be potentially used for. These were initially used in military operations and surveillance. Today, the devices are used extensively for-

  • Building inspections (insulation, roofing, moisture leakage, etc.)
  • Firefighting
  • Autonomous vehicles and automatic braking
  • Measuring skin temperature
  • Conducting scientific research
  • Carrying out industrial inspections and much more

Some Handy Information

The important specifications you should take into account while picking an infrared camera are,

  • Range
  • Resolution
  • Thermal sensitivity
  • Focus
  • Field of view
  • Spectral range


We have given you a fair idea of what you should look for during hot spot detections. You should conduct quantitative testing and record temperature differences between objects that can be compared after making them operate under comparable loads. Every object has a heat signature- the thermal energy emitted by it. You should be able to spot even the slightest differences in heat signatures between objects to arrive at conclusive results that reveal anomalies. It depends on your experience and the training you’ve had. Choose your infrared camera wisely, taking into consideration the specifications we’ve mentioned. Remember, the efficacy of thermal imaging inspection depends a lot on how well you know what to look for during hot spot detections.

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