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Using Voltage Drop Measurements
Tip written by: Infraspection Institute

Accurate confirmation of thermal data is a critical step when performing infrared inspections of energized electrical systems. In this Tip we discuss an advanced verification technique known as a voltage drop measurement.

Loose and deteriorated connections are among the most common defects detected during thermographic inspections of electrical systems. Thermal patterns associated with these defects are characterized by heating at, or adjacent to, mechanical connections within the circuit. Loose connections are frequently found at terminals, lugs, fuse clips and splices.

In most cases, thermographers discovering suspected loose connections will document such hotspots and recommend that the observed exception be investigated and appropriate corrective action be performed. Typically, such investigation is performed at a later time with the circuit de-energized utilizing manual inspection or contact resistance testing.

Another method for confirming loose/deteriorated connections is known as a voltage drop measurement. To perform this test, a digital voltmeter is used to measure voltage across the subject connection with the circuit energized and under load. Loose/deteriorated connections will exhibit an increased voltage drop across the connection due to higher resistance. Observed voltage drop values may then be compared to other similar connections under similar load.

Because voltage drop measurements require contact with energized circuits, this testing should only be performed by qualified persons while observing all necessary safety precautions. Lastly, one should be aware that neither temperature nor voltage drop measurements can predict time of failure for any electrical component. Therefore, suspected loose connections should always be investigated for cause and appropriate corrective action undertaken as soon as possible.

Infrared inspection of electrical distribution systems is one of the many applications covered in the Infraspection Institute Level I Certified Infrared Thermographer^® training course. For course schedules or to obtain a copy of the Standard for Infrared Inspection of Electrical Systems and Rotating Equipment, visit Infraspection Institute online at www.infraspection.com or call us at 609-239-4788.