2. A
three phase voltage system composed three sinusoidal voltages agreeing frequency and
amplitude but differing phase. There are provisions for protective earthing (protective conductor). This voltage not necessarily equal to
the voltage the distribution system but usually lower.2.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.2.2.) This protective measure
necessitates co-ordination type system earthing and the characteristics protective devices. The voltage spreads conductors from
the output the transformer into the distribution system (network) and through this system to
electrical appliances.
There are voltages between conductors (so called phase conductors) L1-L2, L2-L3 and L3-
L1.
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. There are voltages L1-N, L2-N and L3-N. Figure 5. This time depends the voltage existing on
exposed conductive parts case failure insulation. 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. There are three phase voltages the output the
transformer and the distribution system.2 shows diagram secondary winding a
transformer three-phase voltage source. The voltage exists between whichever conductor L1, L2, and neutral
point.
5.
The voltage exists the output the transformer. (Disconnection
must done till the time given Table 4.1 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.3 shows the course instantaneous phase and line voltages during the time of
.
5. These voltages are called line line voltages simply line voltages
Figure 5.4.2.2 Protection automatic disconnection supply
The automatic disconnection the supply the occurrence fault intended prevent
dangerous touch voltage existing for such time considered dangerous
