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
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
If a safety transformer is used the mains voltage is being reduced from 230V
6.2.2 Safety measures against harmful body currents
- 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.