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Tip written by: Infraspection Institute

Infrared thermography is a useful tool for detecting heat patterns caused by overloaded electrical circuits. In this Tip we discuss what constitutes an acceptable load.

Infrared imagers are capable of detecting thermal patterns associated with several electrical deficiencies including overloaded circuits. When viewed with an imager, overloaded circuits will appear warm throughout their entire length with no discrete hot spots. Since it is not possible to determine circuit load from a thermal signature, actual circuit load must be measured with an ammeter.

Once circuit load is known, a question that frequently arises is, ‘How much load is acceptable?’ The answer to this question can be found within the National Electric Code 220-10(b) which provides guidance for circuit loading.

• (b) Continuous and Noncontinuous loads. Where a feeder supplies a continuous load or any combination of continuous or noncontinuous loads, the rating of the over-current device shall not be less than the noncontinuous load plus 125 percent of the continuous load. The minimum feeder circuit conductor size, without the application of any adjustment or correction factors, shall have an allowable ampacity equal to or greater than the noncontinuous load plus 125 percent of the continuous load. NOTE: Exception: Where the assembly including the over-current devices protecting the feeder(s) are listed for operation at 100 percent of their rating, neither the ampere rating of the over-current device nor the ampacity of the feeder conductors shall be less than the sum of the continuous load plus the noncontinuous load.

In other words, for most circuits load should not exceed 80% of conductor ampacity or 80% of the overcurrent device rating. To help ensure accuracy, electric loads should be measured with a true RMS sensing ammeter.

Infrared inspection of electrical equipment is one of the many topics covered in the Infraspection Institute Level I Certified Infrared Thermographer^® training course. This same subject is also the focus of our 16 hour application course, Infrared Inspection of Electrical Systems. For more information or to register for a course, visit Infraspection Institute or call us at 609-239-4788.

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