HT COMBITEST422, Руководство пользователя

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COMBITEST422
EN - 102
12.6. VERIFY OF PROTECTION AGAINST INDIRECT CONTACTS IN TN SYSTEMS
Purpose of the test
Protection against indirect contacts in TN systems must be guaranteed by means of a
protection device against overcurrents (typically MCB or fuse), which switches off the
power supply of the circuit or the electrical equipment in case of faults between an active
part and a ground mass or a protection conductor within a interval not exceeding 5s,
sufficient for the equipments, or in compliance with the times declared in the following
Table 7 . For other countries, please refer to the respective guidelines.
Uo [V] Trip-out time of protection [s]
50

120 0.8
120

230 0.4
230

400
0.2
>400 0.1
Table 6: Tripping times for protection devices
Uo = nominal AC voltage referred to
the system’s ground
The above condition is satisfied by the following relationshisp:
Zs * Ia

Uo
where:
Zs = Fault Loop P-PE impedance which includes the phase winding of the
transformer, the line conductor up to the fault point and the protective
conductor from the fault point to the star center of the transformer
Ia = Tripping current of the protection device within the time specified in Table 7
Uo = nominal AC voltage referred to ground
CAUTION
The instrument must be used to measure fault loop impedance values at
least 10 times higher than the resolution value of the instrument in order to
minimize errors.
Parts of the system to be checked
The test must necessarily be performed on TN and IT systems not protected by differential
devices.
Allowable values
The measurement is aimed at ensuring that, in every point of the system, the following
relationships are satisfied:
PE P
NOM
PE P
MIN PE P MIN
Z
U
C I Ia
−
−
−
 = 
Measured voltage U
NOM
C
MIN
230V-10% < Vmeasured < 230V+ 10% 230V 0.95
230V+10% < Vmeasured < 400V- 10% Vmeasured 1.00
400V-10% < Vmeasured < 400V+ 10% 400V 0.95