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1.5 The Different Types of Safety Tests
1.5.1 Dielectric Withstand Test
The principle behind a dielectric voltage - withstand test is simple. If a product will function when
exposed to extremely adverse conditions, it can be assumed that the product will function in
normal operating circumstances.
Common Applications of the Dielectric Withstand Test:
Design (performance) testing: Determining design adequacy to meet service conditions.
Production Line testing: Detecting defects in material or workmanship during processing.
Acceptance testing: Proving minimum insulation requirements of purchased parts.
Repair Service testing: Determine reliability and safety of equipment repairs.
The specific technique used to apply the dielectric voltage - withstand test to each product is
different. During a dielectric voltage - withstand test, an electrical device is exposed to a voltage
significantly higher than it normally encounters, for a specified duration of time.
During the test, all current flow from the high voltage output to the return is measured. If, during
the time the component is tested, the current flow remains within specified limits, the device is
assumed safe under normal conditions. The basic product design and use of the insulating material
will protect the user against electrical shock.
The equipment used for this test, a dielectric-withstand tester, is often called a "hipot" (for high
potential tester). The "rule of thumb" for testing is to subject the product to twice its normal
operating voltage, plus 1,000 volts.
However, specific products may be tested at much higher voltages than 2X operating voltages +
1,000 volts. For example, a product designed to operate in the range between 100 to 240 volts can
be tested between 1,000 to 4,000 volts or higher. Most "double insulated" products are tested at
voltages much higher than the "rule of thumb".
Testing during development and prototype stages is more stringent than production run tests
because the basic design of the product is being evaluated. Design tests usually are performed on
only a few samples of the product. Production tests are performed on every item as it comes off
the production line.
The hipot tester must also maintain an output voltage between 100% and 120% of specification.
The output voltage of the hipot must have a sinusoidal waveform with a frequency between 40 to
70 Hz and has a peak waveform value that is not less than 1.3 and not more than 1.5 times the
root-mean-square value.
Types of Failures only detectable with a Hipot test
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