METREL MI 3399, Инструкция с упражнениями

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PAT Appliances & Machines Safety Trainer AD 3
– MI 3399
219
Examples of faults
Fault:
Decreased insulation resistance between live parts and isolated accessible
conductive part. Typical reasons are dirt, dust, moisture. Slots and openings in the
enclosure are especially critical.
Result: Dangerous contact voltage on accessible conductive parts not connected to
protective circuit. There is a risk of electrical shock if this part would be touched.
Fault:
Deteriorated insulation between live parts and earthed conductive parts in the
appliance.
Result: Too high leakage current, tripping of RCDs, sparking, overheating of appliance.
Figure 4-7: Examples of insulation faults
Measuring principle / limits:
Measurement on a class I appliance:
Figure 4-8: Example of the insulation test on a Class I appliance
High DC voltage test signal is applied between connected live pins and PE contact of
supply cord. Unearthed accessible conductive parts are NOT included in this test and are
measured as Class II items.