5. That called phase voltage.
Class III equipment
Equipment which protection against electric shock relies supply safety extra low
voltage (SELV) and which voltages higher than those SELV are not generated.2 Protection automatic disconnection supply
The automatic disconnection the supply the occurrence fault intended prevent
dangerous touch voltage existing for such time considered dangerous.
5.2.
There are voltages between conductors (so called phase conductors) L1-L2, L2-L3 and L3-
L1. The voltage exists between whichever conductor L1, L2, and neutral
point.2.3 shows the course instantaneous phase and line voltages during the time of
.2 shows diagram secondary winding a
transformer three-phase voltage source.1 Types system earthing
Before start speak about the types system earthing should know something about
three-phase voltage system, which almost all electric power produced and distributed. The voltage spreads conductors from
the output the transformer into the distribution system (network) and through this system to
electrical appliances. (Disconnection
must done till the time given Table 4. There are voltages L1-N, L2-N and L3-N. These voltages are called line line voltages simply line voltages
Figure 5.2. A
three phase voltage system composed three sinusoidal voltages agreeing frequency and
amplitude but differing phase.FUNDAMENTAL RULES FOR PROTECTION AGAINST ELECTRIC SHOCK 37
installation such way that accessible conductive parts cannot become live the event a
failure the basic insulation. This time depends the voltage existing on
exposed conductive parts case failure insulation. This voltage not necessarily equal to
the voltage the distribution system but usually lower.) This protective measure
necessitates co-ordination type system earthing and the characteristics protective devices.
The voltage exists the output the transformer. Figure 5.2.4. There are three phase voltages the output the
transformer and the distribution system. There are provisions for protective earthing (protective conductor).2.
Class equipment
Equipment which protection against electric shock does not rely basic insulation only,
but which additional safety precautions such double insulation reinforced insulation are
provided.2
