METREL MI 3399, Instruction Manual With Exercises

Page: 215 / 272

PAT Appliances & Machines Safety Trainer AD 3
– MI 3399
215
4.3 Classification of appliances (by protection classes)
According to the design electrical equipment can be divided in three classes. In the table
below the differences between classes are described.
Class
I II III
Marking No marking
Connection to
protection (PE)
conductor of
the installation. Yes.
All accessible
conductive parts (case
etc.) are connected to
the PE connection. No. No connection to mains.
Basic insulation Performed. Performed. Performed / looser limits.
Supplementary
or reinforced
insulation Not needed in
general.
Needed if there are
accessible unearthed
conductive parts
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.
Performed. Not needed.
Supply cord Three pole (L,N, PE). Can be two pole. Two pole.
Notes Installation must have
adequate earth
resistance. Must be supplied from a
SELV (safety low
voltage) source, typically
12 V or 24 V.
Table 4-1: Classification of appliances
4.4 Portable electrical appliances
– measurements
Basic test that need to be conducted while the portabe device is powered off:
1. Visual inspection
2. Earth bond/earth continuity
3. Insulation resistance (with or without Probe)
4. Sub-Leakage (optionaly)
If all conducted test above passed, the portable device should be turned on and the following tests
performed:
1. Leakage (Differential or touch)
2. Polarity
3. PRCD
4. Functional
The probe test is conducted on Class II devices (flatiron, radio with an external antenna,
…)
4.4.1 Visual inspection
Visual inspection of the equipment is intended to confirm that there are no visible signs
of damage or defects. Electrical testing often does not disclose failures that become
apparent on visual inspection. The visual inspection discloses most of faults! A thorough
visual check must be carried out before each electrical safety test.
10
Class I equipment can be combined with class II safety measures!