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Dimensions
Section 12
11
Motor starters
In general miniature circuit breakers can give only short circuit protection to motor
loads due to the high starting currents which may be encountered; typically 3 - 12
times full load current (FLC).
Assumptions
The tables give recommended MCB ratings for motors up to 37kW based on the
following assumptions:
n
Direct-on-line starting
Starting current = 7 x FLC
Run up time = 6seconds, motors <3kW
10 seconds, motors < 22kW
Running currents = average values only (individual manufacturer’s figures will
vary). four pole motors, i.e. speed approx. 1500rpm
For higher inertia loads, i.e. hoists or fans, run up times may be considerably
longer than those assumed above. The rating of the MCB must take account
of the greater run up time and starting current. The required MCB rating can be
determined by reference to time/current curves (consult us).
n
Star/delta starting
Since, during the changeover from star to delta, a high current surge in the order
of DOL values may be met, the MCB rating selected should be the same as that
recommended for DOL starting.
Table 1 - 3 phase 415Vac D.O.L. starting
Recommended MCB
kW hHp Running I
C60HB
C60HC
C60HD
0.12 0.166 0.65
2
2
1
0.18 0.25 0.7
2
2
1
0.25 0.33 0.87
4
2
1
0.37 0.5 1.35
4
4
2
0.55 0.75 1.55
4
4
2
0.75 1.0 1.93
6
4
4
1.1 1.5 2.5
6
6
4
1.5 2
3.5
10
10
6
2.2 3
4.8
16
10
10
3
4
6.4
20
20
10
3.75 5
7.8
25
25
16
4
5.5 8.1
25
25
16
5.5 7.5 11
32
32
16
7.5 10
14.4
50
50
20
9.33 12.5 17.3
63
50
20
11 15
21
63
63
25
13 17.5 25
-
-
32
15 20
28
-
-
40
18.5 25
35
-
-
50
22 30
40
-
-
50
30 40
54
-
-
63
37 50
65.5
-
-
-
Table 2 - 1 phase 240Vac D.O.L. starting
kW Hp Running I
C60HB
C60HC
C60HD
0.12 0.166 0.95
4
2
1
0.18 0.25 1.5
4
4
2
0.25 0.33 1.7
6
4
2
0.37 0.5 3
10
6
4
0.55 0.75 4.5
16
10
6
0.75 1
5.5
16
16
10
1.1 1.5 8.5
25
25
16
1.5 2
10.5
32
32
20
2.2 3
15.5
40
40
25
3
4
20
63
63
32
3.75 5
24
-
63
40
5.5 7.5 34
-
-
50
6.3 8.5 36.5
-
-
63
7.5 10
45
-
-
63
11 15
66.5
-
-
-
For use in conjunction with
motor starters and transformers
Miniature circuit
breakers