Extech Instruments 7630 Operation Manual page 14

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
• Weak Insulating Materials
• Pinholes in Insulation
• Inadequate Spacing of Components
• Pinched Insulation
1.5.1.1 AC Dielectric Withstand Test
Please check with the Compliance Agency you are working with to see which of the two types
of voltages you are authorized to use. In some cases, a Compliance Agency will allow either
AC or DC testing to be done. However, in other cases the Compliance Agency only allows
for an AC test.
Many safety agency specifications allow either AC or DC voltages to be used during the hipot
test. When this is the case, the manufacturer must make the decision on which type of
voltage to utilize. In order to do this it is important to understand the advantages and the
disadvantages of both AC and DC testing.
AC testing characteristics
Most items that are hipot tested have some amount of distributed capacitance. An AC
voltage cannot charge this capacitance so it continually reads the reactive current that flows
when AC is applied to a capacitive load.
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