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must be supplied, the current required by the instrument will be much larger than the current
used in the DC test. This will increase the danger to the operator.
2.3.2 Characteristics of Direct Current (DC) Test
During the DC withstand voltage test, the stray capacitance on the DUT is filled. The capacitive
current caused by the DC withstand voltage test will drop to zero after the stray capacitance is
filled.
2.3.2.1 Advantages of Direct Current (DC) Testing
1. Once the stray capacitance on the DUT is full, only the actual leakage current of the DUT will
remain. The DC withstand voltage test can clearly show the actual leakage current of the DUT.
2. Another advantage is that only the charging current of the DUT needs to be supplied in a short
time, and the current required at other times is very small, so the current capacity of the
instrument is much lower than the current capacity required during the AC withstand voltage
test. .
2.3.2.2 Disadvantages of Direct Current (DC) Testing
1. Unless there is no electric capacity on the DUT, the test voltage must start from "zero" and
rise slowly to avoid excessive charging current. The larger the electric capacity, the longer the
ramp-up time, the longer it can increase The lower the voltage. When the charging current is too
large, it will definitely cause the tester to misjudge and make the test result incorrect.
2. Since the DC voltage test will charge the test object, after the test, the test object must be
discharged before the next step.
3. Unlike the AC test, the DC withstand voltage test can only be tested with a single polarity. If
the product is to be used under AC voltage, this disadvantage must be considered. This is why
most safety agencies recommend the use of AC withstand voltage tests.
In the AC test, the peak value of the voltage is 1.4 times that displayed by the meter, which is not
displayed by ordinary meters, and cannot be reached by DC withstand voltage. Therefore, most
safety regulations require that if a DC withstand voltage test is used, the test voltage must be
increased to an equivalent value.
2.4 Insulation resistance test
The insulation resistance test mainly measures the resistance between the live wire of the
appliance and the case. The measurement method is based on the principle of Ohm's law, adding
a voltage between the live wire and the case, and then measuring the voltage and current values,
and then calculating the resistance value according to Ohm's law. Usually, a larger constant
voltage (500V or 1000V DC) is applied and maintained for a specified period of time as the test
standard. If the resistance is kept within the specified specifications within the specified time, it
can be determined that the appliance is operating under normal conditions, and the appliance
