Iso-Tech IMT-3300 Bedienungsanleitung Seite 9

RCD 30mA
For this example the maximum value is 1667Ω, the loop
tester reads 12.74Ω and consequently the condition RA is
≤ 50/Ia is met. It is also important to test the operation of
the RCD using a dedicated RCD tester in accordance with
the international standard IEC60364 for a TN system. The
following condition shall be fulfilled for each circuit.
Zs ≤ Uo/Ia where Zs is the earth fault loop impedance voltage
is the nominal voltage between phase and earth and Ia is
the current that causes the automatic disconnection of the
protective device within the time stated in the following table.
Uo(Volts)
120
230
400
>400
Note:
When the protective device is a residual current device (RCD),
Ia is the rated residual operating current IΔn.
For instance in a TN system with a nominal mains voltage of
Uo = 230V protected by type gG fuses the Ia and maximum Zs
values could be:
Fig 6
T(seconds)
0.8
0.4
0.2
0.1
Rating(A) Disconnecting
Ia(A)
6 28
10 46
16 65
20 85
25 110
32 150
40 190
50 250
63 320
80 425
100 580
If the prospective fault current is measured, its value must be
higher than the Ia value of the protective device concerned.
The maximum value of Zs for this example is 2.10Ω (16 amp
gG fuse, 0.4 seconds). The loop tester reads 1.14Ω and
consequently the condition Zs ≤ Uo/Ia is met.
— 9 —
Time 5s Disconnecting Time 0.4s
Zs(Ω) Ia(A)
8.20 47
5.00 82
3.60 110
2.70 147
2.10 183
1.53 275
1.21 320
0.92 470
0.71 550
0.54 840
0.39 1020
Fuse gG 16A
Zs(Ω)
4.90
2.80
2.10
1.56
1.25
0.83
0.72
0.49
0.42
0.27
0.22
Fig 7