METREL MI 3399, Инструкция с упражнениями

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PAT Appliances & Machines Safety Trainer AD 3
– MI 3399
223
Measurement on a class II appliance.
Figure 4-14: Example of sub-leakage test on a Class II appliance
AC test signal is applied between connected live pins and accessible conductive parts
not connected to protective circuit. Each accessible part shall be tested alone.
Notes:

On/Off switches must be closed. If after switches were closed all safety relevant
parts are not included the results will be impaired. This is often the case in
electronic or relay driven On/Off circuits. In this case or if in doubt leakage current
tests can be performed as an alternative.

This test cannot be applied on Class II appliances without accessible conductive
parts.

Appliances with leakage currents >3.5mA should be marked.

This measurement returns similar results as leakage tests on powered appliances.
The sub-leakage result is usually higher (up to 2 times) because of connected L
and N conductors.

The sub-leakage test is suitable for IT appliances (at connected mains voltage the
test must last longer to allow booting up the equipment).
4.4.5 Leakage current tests
– general
Scope of test
In this test the sum of leakage currents caused by appliance insulation resistances
(resistive currents through the insulation material, fault currents through decreased
insulation) and capacitances (capacitive leakage current) is checked. Even leakage
currents in range of mA are dangerous. The danger increases if the installation is not
properly earthed.
Excessive leakage currents are most often caused by deterioration of the appliance
insulation (pollution, ageing, moisture) or faults in mains circuits of appliances.
In general three leakage currents are measured: the differential leakage current, the PE
conductor (direct) leakage current and the touch leakage current.
4.4.6 PE conductor leakage current test
This test is sometimes called direct leakage test too.