KYORITSU 4120A User Manual
Page 15
L1
L2
L3
N
PE
R
R
O
RCD 30mA
― 13 ―
For this example max value is 1667Ω, the loop tester reads 12.74Ω, it
means that the condition RA
＜
50/Ia is respected.
It is fundamental for this example to test also the RCD to ensure that
operation takes place quickly enough to respect the safety requirements. In
order to do it, can be used the RCD tester model 5406A.
According to the international Standard IEC 60364 for TN system the
following condition shall be fulfilled for each circuit:
Zs
＜
Uo/Ia
Where:
¡
Zs is the Fault loop impedance.
¡
Uo is the nominal voltage between phase to earth.
¡
Ia is the current causing the automatic disconnection of the protective
device within the time stated in table as follows:
Note:
● For a distribution circuit a disconnection time not exceeding 5s is
permitted.
● When the protection device is a residual current device (RCD), Ia is
the rated residual operating current I
⊿
n.
Uo (Volts)
120
230
400
>400
T (seconds)
0.8
0.4
0.2
0.1
Fig.8
Practical example of verification of the protection in a TT system according
to the international Standard IEC 60364.