Low Voltage Switch Gear
Appendix
101
■
Rated currents of 3-phase motors (approx. figures for squirrel-cage motors)
Minimum fuse size for protection of 3-phase motors
The maximum size is determined by the requirements of the switchgear or overload relay.
The rated motor currents are for standard 1500 r.p.m. 3-phase enclosed ventilated and totally enclosed fan-cooled motors.
D.O.L. starting:
Maximum starting current 6 x rated motor current. Maximum starting time 5 s.
Y/D starting:
Maximum starting current 2 x rated motor current. Maximum starting time 15 s.
Set overload relay in the phase lead to 0.58 x rated motor current.
Rated fuse currents for Y/D starting are also valid for 3-phase motors with slip-ring motors.
For higher rated currents, starting currents and/or longer starting times, larger fuses are required.
Table is valid for “slow” and/or “gL” fuses (DIN VDE 0636).
For NH fuses with aM characteristics, fuses = rated current is selected.
Motor rating
230 V
400 V
415 V
Rated
motor
current
Fuse
starting
D.O.L.
Y/
∆
Rated
motor
current
Fuse
starting
D.O.L.
Y/
∆
Rated
motor
current
Fuse
starting
D.O.L.
Y/
∆
kW
cos
ϕ
η
%
A
A
A
A
A
A
A
A, BS
A, BS
0.06
0.7
58
0.37
2.0
-
0.21
2.0
-
0.21
2.0
2
0.09
0.7
60
0.54
2.0
-
0.31
2.0
-
0.30
2.0
2
0.12
0.7
60
0.72
4.0
2
0.41
2.0
-
0.40
2.0
2
0.18
0.7
62
1.04
4.0
2
0.6
2.0
-
0.58
2.0
2
0.25
0.7
62
1.4
4.0
2
0.8
4.0
2
0.8
4.0
2
0.37
0.72
66
2.0
6.0
4
1.1
4.0
2
1.1
4.0
2
0.55
0.75
69
2.7
10.0
4
1.5
4.0
2
1.5
6.0
4
0.75
0.79
74
3.2
10.0
4
1.9
6.0
4
1.8
6.0
4
1.1
0.81
74
4.6
10.0
6
2.6
6.0
4
2.6
10.0
6
1.5
0.81
74
6.3
16.0
10
3.6
6.0
4
3.5
16.0
10
2.2
0.81
78
8.7
20.0
10
5.0
10.0
6
4.8
16.0
10
3.0
0.82
80
11.5
25.0
16
6.6
16.0
10
6.4
20.0
16
4.0
0.82
83
14.8
32.0
16
8.5
20.0
10
8.2
20.0
16
5.5
0.82
86
19.6
32.0
25
11.3
25.0
16
10.9
25.0
20
7.5
0.82
87
26.4
50.0
32
15.2
32.0
16
14.6
35.0
25
11.0
0.84
87
38.0
80.0
40
21.7
40.0
25
20.9
50.0
32
15.0
0.84
88
51.0
100.0
63
29.3
63.0
32
28.2
80.0
40
18.5
0.84
88
63.0
125.0
80
36.0
63.0
40
35.0
80.0
50
22.0
0.84
92
71.0
125.0
80
41.0
80.0
50
40.0
80.0
50
30.0
0.85
92
96.0
200.0
100
55.0
100.0
63
53.0
100.0
80
37.0
0.86
92
117.0
200.0
125
68.0
125.0
80
65.0
125.0
80
45.0
0.86
93
141.0
250.0
160
81.0
160.0
100
78.0
125.0
80
55.0
0.86
93
173.0
250.0
200
99.0
200.0
125
96.0
160.0
100
75.0
0.86
94
233.0
315.0
250
134.0
200.0
160
129.0
250.0
160
90.0
0.86
94
279.0
400.0
315
161.0
250.0
200
155.0
250.0
160
110.0
0.86
94
342.0
500.0
400
196.0
315.0
200
189.0
315.0
200
132.0
0.87
95
401.0
630.0
500
231.0
400.0
250
222.0
355.0
250
160.0
0.87
95
486.0
630.0
630
279.0
400.0
315
269.0
355.0
315
200.0
0.87
95
607.0
800.0
630
349.0
500.0
400
337.0
450.0
355
250.0
0.87
95
-
-
-
437.0
630.0
500
421.0
500.0
450
315.0
0.87
96
-
-
-
544.0
800.0
630
525.0
630.0
560
400.0
0.88
96
-
-
-
683.0
1000.0
800
-
-
-
450.0
0.88
96
-
-
-
769.0
1000.0
800
-
-
-
500.0
0.88
97
-
-
-
-
-
-
-
-
-
560.0
0.88
97
-
-
-
-
-
-
-
-
-
630.0
0.88
97
-
-
-
-
-
-
-
-
-
