MODULE V Electrical engineering - Basics Page 39

6.2 Safety measures for dealing with electric current

The safety measures for dealing with electric current can be divided into three groups:


6.2.1 Safety measures against dangerous contact

• Safety insulation
  Those parts of electric devices or machines (e.g. hand drills) that have contact with electric current have to be particularly insulated (with e.g. rubber or plastic) so that if one unintentionally touches them no harm is done.
  -> As soon as e.g. the insulation of an extension cord is damaged it has to be repaired.
  
  
• Protective disconnection
  Disconnection transformers disconnect electric devices from the public electricity mains in case of an accident. Electric devices that are connected to disconnection transformers are automatically being disconnected from their grounding connection in the case of an internal insulation breakdown so that no return flow of electric current through the human body to the earth can occur anymore.
  
  
• Protective extra-low voltage
  If a safety transformer is used the mains voltage is being reduced from 230V to 50V.

• Protective grounding
  If the parts of an electric device or machine that do not conduct current are connected to protective grounding through a ground electrode then in case of an accident the fuse of the circuit interrupts the current flow. Protective grounding conductors are also called PE-conductors (PE = protection earth). The colour of the PE-conductor insulation is normally green and yellow.
  
  
• Earth-leakage circuit breaker or fault current protection switch
  The earth-leakage circuit breaker, also called "FI-switch", disconnects the electricity mains that is located behind it from the power supply as soon as there is a fault current of e.g. 30mA.