6
Section 1
Introduction and Safety
An Introduction to Dielectric Withstand Testing with the HT-S
The continuity test/dielectric withstand test is a production line test which is recognized by safety
agencies worldwide as a valid criterion of safe assembly of end-use equipment. The test ensures that the
primary circuit power and ground conductors were properly wired and connected for safe operation. It also
applies a high-voltage potential between power and ground conductors to make sure that no unintentional
leakage or arcing paths exist between power and ground. The test consists of a ground continuity check, a
leakage current check and a high voltage check. It is non-destructive to the equipment under test, and can
be accomplished in a short time.
The purpose of dielectric testing: Dielectric testing is a simple, non-destructive method of
verifying the adequacy of electrical insulation to withstand the sort of transients that can occur during
transient (surge) events. In addition, the dielectric test can verify that the insulation in question has an
adequate amount of performance "headroom". This is necessary to ensure that the insulation does not fail
because of degradation of the insulation due to aging, moisture, wear due to vibration, etc.
The method of dielectric testing: A high voltage (typically 1000 Volts or higher) is applied
between two conductors that are "supposed" to be electrically insulated from each other. If the two
conductors (an insulated "live" wire, and a metal enclosure, for example) are completely isolated from each
other, then the application of a large voltage difference between the two conductors will not allow current
to flow between the conductors. The insulation will "withstand" the application of a large voltage potential
between the two conductors - hence the term "dielectric withstand test". In general, there are two results of
the test that are considered a failure of the insulation: (1) excessive current flow during the test due to low
insulation resistance of the insulating material which separates the two conductors, and (2) an abrupt
dielectric breakdown due to electrical arcing or discharge, either through the insulation material, over the
surface of the insulation material, or a discharge through air.
The determination of a suitable test voltage: If the test voltage is too low, the insulation material
in question will not be adequately stressed during the test. This could cause inadequate insulation to pass
the test, and be considered acceptable. On the other hand, if the test voltage is too high, then the test could
cause permanent damage to an insulation material that is otherwise adequate for the application. A general
"rule of thumb" that is used for the testing of mains wiring which operates at voltages of 120-240Vac is
1000V plus two times the operating voltage. Using this rule, 120V wiring would be tested using a voltage
of 1240Vac.
Duration of the test: Generally, the test voltage is applied for one minute, in order to adequately
stress the insulation. Many standards allow the test duration to be reduced to 1 second for production-line
testing in order to accommodate large-volume production testing. In this case, standards quite often require
that the test voltage be increased by 20% in order to ensure that the shorter test duration of one second will
adequately test the insulation in question.
Safety Precautions
The dielectric withstand test generates voltages of up to 2000 Volts AC (HT-2000S & HT-3000S),
up to 3000 Volts AC(HT-4200S), up to 2800 Volts DC (HT-2800S & HT-3000S) or up to 4200 Volts DC
AC (HT-4200S) at potentially lethal current levels. Currents of as little as 5 mA at 120V can cause death,
and the HT-S is capable of generating 20mA AC at up to 2000 Volts (10mA at up to 3000Volts for HT-
4200S), and 5mA DC at up to 2800 Volts (up to 4200 Volts for HT-4200S). The HT-S has been designed
to minimize exposure to high voltages. However, the potential for serious injury or death exists and
personnel should be aware when they conduct this test.
Any use of this equipment other than as specified in this manual may result in a safety hazard.
