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Protection class
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Protection against electric shock
1. Protection against direct and indirect contact – general terms
The protection against electric shock on electric equipment as well as their components are divided into the following parts:
Protection against direct contact with live parts concerns all measures for the protection of human beings and animals against hazards which result from direct contact with live parts of electric equipment and their components.
Protection against indirect contact is the protection of human beings and animals against hazards which result from contact of live parts of electric equipment as well as components thereof, which have become live due to an insulation failure.
2. Protection against direct contact with live parts e.g. of a fuseholder.
The data sheets of the relevant components inform about the taken measures.
3. Protection against indirect contact
Measures for the protection against indirect contact on electrical equipment are defined according to IEC 61140 by the 4 protection classes 0, I, II, III. Each protection class includes two protection measures. Even if one of these measures should fail, no electric shocks will occur.
Protection Class
Main protective measures
0
1. Basic insulation between live parts and accessible conductive parts.
2. Earth-free location, non-conducting environment.
I
1. Basic insulation between live parts and accessible conductive parts.
2. Means are provided for the connection of accessible conductive parts of the equipment to the protective (earthing) conductor in the fixed wiring of the installation in such a way that accessible conductive parts cannot become live in the event of a failure of the basic insulation.
II
1. Basic insulation between live parts and accessible conductive parts.
2. Additional insulation. Basic and supplementary insulation are summarised under the term “double insulation”. Under certain circumstances also a “reinforced insulation» (single insulation system) may guarantee an equivalent protection against electric shock as a “double-insulation” does. No terminal for a protective conductor is allowable. A possibly existing protective conductor must not be connected and has to be insulated like any live part.
III
1. Functional insulation.
2. Supply at safety extra-low voltage SELV (the circuit is isolated from the mains supply by such means as a safety isolating transformer). The protection against electric shock is in this case completely based on the supplying by SELV-circuits (U ≤ 42 V). Higher voltages are not generated in the equipment. No terminal for a protective conductor is allowable.
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