Lexicon DIY-Knowledge

Electrical safety

Elektrische Sicherheit

Seguridad eléctrica

Sécurité électrique

The requirements for electrical safety are set out in the protective safety measures against high contact voltages in DIN-EN 50 144 and EN 5144. Electric power tools must conform to one of the protection classes in order to prevent contact voltages in case of defect.

Class I
Basic safety insulation with protective conductor terminal. Not often found in power tools today!

Class II 
Total insulation: double insulation or the equivalent, without protective conductor terminal.

Full insulation: double insulation or the equivalent, without protective conductor terminal. All machine parts which can possibly be touched during operation are additionally insulated. Protection against electric currents from inside and outside. This means: total insulation also protects the operator against contact voltage from a hidden power line he has drilled into.

Class III
Protective low voltage ? protection by electrical separation of circuits: Required for wet sanding, when working in boiler plants and for immersion vibrators for concrete.

(See also Protection class I, II, III)

Electric arc

Electric arcs generate heat which is used for welding. Arc welding is a type of fusion welding. An electric flow of current heats two electrodes on their point of contact. If these two electrodes are separated, an electric arc remains standing in the ionised air between them which generates even more heat and makes melting fusion possible. Switch contacts can experience the same phenomenon if the contact resistances allow the generation of excess heat, especially if direct current is being connected. A standing electric arc can destroy switch contacts. For this reason switches indicate their maximum capacities for direct and alternating current.