Variants of improper earthing. 
<ul><li>1) PE creating in outlet. Quite widespread in ex-USSR countries, cause the lion's share of Soviet apartment blocks with hard concrete walls (even for modern rotary hammers) have no PE wire at all. It was expensive in such giant volumes of work, so nobody did "useless work" puting PE wires.</li>
<li>2) RCD is, but PE wire is missing. RCD can detect only if someone touch metal cover and get electric shock.</li>
<li>3) PE wire is, but RCD is missing. Fuse will trip only if the gauge of yellow-green wire is enough. Otherwise cover will have danger potential for human on it and wires will heat.</li>
<li>4) RCD and earthing are missing. If insulation will be spoiled, nothing will detect it. If human will touch it, nothing will protect him. If nobody help him intime, human will lose his life.</li></ul>
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