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close this bookIntroduction to Electrical Engineering - Basic vocational knowledge (Institut für Berufliche Entwicklung, 213 p.)
close this folder9. Protective Measures in Electrical Installations
close this folder9.2. Measures for the Protection of Man from Electric Shock
View the document9.2.1. Protective Insulation
View the document9.2.2. Extra-low Protective Voltage
View the document9.2.3. Protective Isolation
View the document9.2.4. Protective Wire System
View the document9.2.5. Protective Earthing
View the document9.2.6. Connection to the Neutral
View the document9.2.7. Fault-current Protection

9.2.1. Protective Insulation

For electrical household appliances and portable tools (e.g. electric hand-drilling appliances), the electrical protective insulation is a very effective protection from electric shock. The emergence of a contact voltage is practically avoided by the special arrangement of the insulation. Fig. 9.2. shows two methods of arranging a protective insulation. For example, an electric hand-drilling appliance can be provided with a plastic enclosure (protective insulating covering) and the metallic gear and drill chuck can be connected with the motor by means of a clutch of insulating material (protective intermediate isulation). For this purpose, special requirements must be specified for the mechanical, thermal, electrical and chemical stability of the insulating materials to be used. At accessible points of live parts, which do not belong to the service circuit, a protective conductor must not be connected. Devices with protective insulation may be marked with two squares, an outer one and an inner one. ()

Fig. 9.2. Protective insulation

a) protective insulating covering

b) protective intermediate insulation


Operational insulation


Metal enclosure


Protective insulation