KYORITSU 6050 - Manual (Page 17)

̶ 15 ̶
Uo (Volts)
120
230
400
>400
T (seconds)
0.8
0.4
0.2
0.1
Fig.11
Practical example of verification of the protection is a TT system according to
the international Standard IEC 60364.
For this example the maximum value is 1667Ω,the loop tester reads 12.74
Ωand consequently the condition RA is <_ 50/la is met.
It is fundamental for this example to test also the RCD to ensure that
operation takes place quickly enough to respect the safety requirement.
According to the international Standard IEC 60364 for TN system the
following condition shall be fulfilled for each circuit:
Zs<_Uo/la
Where;
Zs is the earth fault loop impedance.
Uo is the nominal voltage between phase and earth.
la is the current that causes the automatic disconnection of the protective
device within the time stated in the following table.