Extech Instruments 7470 Operation Manual page 16

to AC.
When performing AC hipot tests the product under test is actually tested with peak
voltages that the hipot meter does not display. This is not the case with DC testing
since a sinewave is not generated when testing with direct current. In order to
compensate for this most safety agencies require that the equivalent DC test be
performed at higher voltages than the AC test. The multiplying factor is somewhat
inconsistent between agencies which can cause confusion concerning exactly what
equivalent DC test voltage is appropriate.
1.6.2. Insulation Resistance Test
Some "dielectric analyzers today come with a built in insulation resistance tester.
Typically, the IR function provides test voltages from 500 to 1,000 volts DC and
resistance ranges from kilohms to gigaohms. This function allows manufacturers to
comply with special compliance regulations. BABT, TÜ V and VDE are agencies that
may under certain conditions, require an IR test on the product before a Hipot test is
performed. This typically is not a production line test but a performance design test.
The insulation resistance test is very similar to the hipot test. Instead of the go/no go
indication that you get with a hipot test the IR test gives you an insulation value usually
in Megohms. Typically, the higher the insulation resistance value the better the
condition of the insulation. The connections to perform the IR test are the same as the
hipot test. The measured value represents the equivalent resistance of all the
insulation which exists between the two points and any component resistance which
might also be connected between the two points.
Although the IR test can be a predictor of insulation condition it does not replace the
need to perform a dielectric withstand test.
1.6.3. Ground Bond Test
The Ground Bonding test determines whether the safety ground circuit of the product
under test can adequately handle fault current if the product should ever become
defective. A low impedance ground system is critical in ensuring that in case of a
product failure, a circuit breaker on the input line will act quickly to protect the user from
any serious electrical shock.
International compliance agencies such as CSA, IEC, TÜ V, VDE, BABT and others,
have requirements calling out this test. This test should not be confused with low
current continuity tests that are also commonly called out in some safety agency
specifications. A low current test merely indicates that there is a safety ground
connection. It does not completely test the integrity of that connection.
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