Major tech MT350 Руководство по эксплуатации - Страница 6
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7. MEASUREMENT OF LOOP IMPEDANCE AND PROSPECTIVE
SHORT CURRENT
If there is a RCD or fuse in the circuit, they must be bridged out prior to
testing the loop impedance.
According to IEC 60364, every loop should meet the formula: Ra≤50/la
Ra: loop impedance
50: max of touch voltage
Ia: the current than can make the protection device break down the circuit
in 5 seconds.
When protection device is RCD, Ia is rated residual current IΔn.
IΔn
10
Ia(50v)
5000
Ia(25v)
2500
According to IEC 60364, every loop should meet the formula: Zs ≤ Uо/la
When protection device is FUSE, Uо=230V, la and Zsmax:
Rated
Current
6
10
16
20
25
32
40
50
63
80
100
Prospective short current must be bigger than la.
6
30
100
1667
500
833
250
Break time (5s)
Ia(A)
Zs(Ω)
28
8.2
46
5
65
3.6
85
2.7
110
2.1
150
1.53
190
1.21
250
0.92
320
0.71
425
0.54
580
0.39
300
500
167
100
83
50
Break time (0.4s)
Ia(A)
47
82
110
147
183
275
320
470
550
840
1020
1000
mA
50
Ω
25
Ω
Zs(Ω)
4.9
2.8
2.1
1.56
1.25
0.83
0.72
0.49
0.42
0.27
0.22