FUNDAMENTAL RULES FOR PROTECTION AGAINST ELECTRIC SHOCK 45
d) Earthing protective conductors
The international standard requires earthing the protective conductor PEN conductor
near each power transformer generator the installation and wherever the supply system
where other effective connections exist.c.6 Protective measures systems
In system the following electrical condition shall fulfilled:
RA UL
where
RA earthing resistance the earthing exposed conductive parts,
Ia the operating current the protective device the disconnecting time (which is
for overcurrent protective devices, for residual current protective devices),
UL the conventional voltage limit, e.e.2.7 Protective measures systems
The systems shall built such way comply with the following conditions: In
case occurrence first fault (on insulation electrical appliance), when the fault current is
low the following condition shall fulfilled:
RA UL
where
RA the earthing resistance the earthing exposed conductive parts,
Id the fault current the first fault negligible impedance between phase conductor,
UL the conventional voltage limit, i.
5.
There are many other conditions which are fulfilled for the right function protection
in system, but cannot pay attention them for the shortage time and space.g.2.
5. a.2.3 The maximum disconnecting time case fault system
Uo (V) (s)
120 0,8
230 0,4
277 0,4
400 0,2
>400 0,1
.2. a.
In system the use the residual-current protective devices preferably recognized and
also the overcurrent protective devices may used. Czech standards require earthing defined distances of
the length the line. for normal condition.
Table 5.2.c
