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TECHN I CAL DATA
MCB AP P L I CAT I ON
217
TRANSFORMERS
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Transformers produce inrush currents when they are switched on, typically 15
times the normal running current.
The tables below show the recommended MCB rating for single phase (230V)
and 3 phase (400V) transformers.
SINGLE PHASE 230V AC SUPPLY
TRANSFORMER MCB RATING (A)
RATING (VA)
Type B
Type C
Type D
50
6
6
6
100
6
6
6
200
6
6
6
300
10
6
6
400
10
6
6
500
16
10
6
750
16
10
6
1000
32
16
10
2500
63
32
16
5000
–
63
32
7500
–
–
50
10000
–
–
63
THREE PHASE 400V AC SUPPLY
TRANSFORMER MCB RATING (A)
RATING (VA)
Type B
Type C
Type D
500
6
6
6
750
6
6
6
1000
10
6
6
2000
16
10
6
3000
32
16
10
4000
32
20
10
5000
40
32
16
7500
63
32
16
10000
–
50
32
15000
–
63
32
20000
–
–
50
25000
–
–
63
30000
–
–
63
The above information applies to MCBs supplying transformers irrespective of
the load on the secondary circuit. If the MCBs are on the secondary side of
the transformer, they do not see the inrush current and so nuisance tripping
does not occur.
POLESTAR & LOADSTAR MCB APPLICATIONS – TRANSFORMERS & LIGHTING LOADS
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LOW VOLTAGE LIGHTING
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Low voltage lighting is generally supplied via a transformer. If MCBs are used on
the primary (input) side of the transformer, then the information given in the
section below left is applicable. If MCBs are used on the secondary (output)
side, then no special precautions are necessary.
FLUORESCENT LIGHTING
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Fluorescent lighting can also produce high inrush currents, especially when
electronic ballasts are used. However, the duration of the inrush current is
generally less than 1ms, so that the current may fall to normal levels before the
MCBs have had time to react.
It is recommended that fluorescent lighting is protected by type C MCBs, which
give a good level of protection whilst avoiding the risk of nuisance tripping.
MCB RATING (A) MAXIMUM NUMBER OF LAMPS AT 230V
TYPE C
36
W
58
W
80
W
6
10
6
5
10
16
10
8
16
26
16
13
20
33
20
17
32
53
33
27
40
66
41
34
50
83
51
42
63
105
65
54
HIGH-PRESSURE SODIUM LAMPS
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High-pressure sodium lamps draw current of more than 30 times their normal
running currents for the first few milliseconds after start up.
MCB RATING (A) MAXIMUM NUMBER OF LAMPS
TYPE B
150
W
250
W
400
W
6
–
–
–
10
1
–
–
16
1
1
–
20
2
1
–
32
3
2
1
40
4
2
1
50
5
3
1
63
6
4
2
TYPE C
6
1
–
–
10
1
1
–
16
2
1
–
20
3
2
1
32
5
3
1
40
6
4
2
50
8
5
2
63
10
7
3
TYPE D
6
2
1
–
10
3
2
1
16
5
3
1
20
6
4
2
32
10
7
3
40
13
8
4
50
16
11
5
63
21
14
7
It is recommended that type D MCBs are used where possible, as they will
give good thermal protection without suffering from nuisance tripping.