GSC60
EN - 119
12.8. VERIFY OF PROTECTION AGAINST INDIRECT CONTACTS IN IT SYSTEMS
In IT systems the active parts must be isolated from the ground or be connected to earth
through an impedance of sufficiently high value. In the case of a single earth fault current
of the first fault is weak and therefore it is not necessary to interrupt the circuit. This
connection can be made to the neutral point of the system or to an artificial neutral point. If
there is no neutral point, can be connected to earth through an impedance of a line
conductor. It must, however, take precautions to avoid the risk of harmful physiological
effects on people in contact with conductive parts simultaneously accessible in the case of
a double earth fault.
Purpose of the test
Verify that the impedance of the ground probe in which the mass are connected satisfyteh
following relationship:
LdE
UIZ *
where:
Z
E
= L-PE impedance of the ground probe in which the mass are connected
Id = L-PE current of first fault (typically expressed in mA)
U
L
= Limit contact voltage 25V or 50V
Parts of the system to be checked
The earth system under operating conditions. The verification should be performed without
disconnecting the ground probes.
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