Measuring Insulation Resistance - UEi DMEG3/IRT3 Instruction Manual

Measuring Insulation Resistance

Insulation resistance testing (IRT) is the process of evaluating
an insulating material's integrity. Any time you use IRT
procedures; you will be applying a relatively high DC voltage
(250, 500 or 1000 Volts) to two separate conducting paths. For
example, the "conducting paths" might be the hot and neutral
wires in a cable set. With this voltage applied, your meter will
measure the extremely small amount of current that flows
between the two paths. Using the principles of Ohm's law, the
resistance value is displayed.
What needs to be tested: All insulating materials begin
deteriorating from the day they are made. Knowing this, a
wide variety of insulation specifications have been created to
accommodate different environments in which they will be
used. Some of those ratings refer to environmental conditions
such as indoor use, outdoor use, chemical resistant, high or low
temperature, maximum voltage or current ratings and many
more. When insulating materials are subjected to conditions
other than what they are rated for, and as time takes its toll,
deterioration accelerates.
Frequently the life span of an insulating material is known to
be less than the life span of the appliance it is being used in.
Motor windings are a good example. Industrial manufacturing
equipment, commercial refrigeration systems and other
processes require predictive and preventive maintenance (PM)
procedures to ensure uninterrupted operation. Insulation
resistance testing should be part of that maintenance process.
IRT procedures are recommended, and often documented by
numerous engineering and maintenance organizations such as
IEEE, NETA and IEC. You can access these organizations and the
documents they have produced related to insulation resistance
testing through the internet. Some documents are fee-based.
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