Protection with fuses

Protection with fuses2018-10-03T12:35:26+00:00

This standard states that the power of the transformers is calculated according to the following formula:

P(VA)=U (V) X I (A)

Thus, the following table shows the values of the fuses to be connected to the secondary circuit (output), recommended for the protection of most popular transformers:

POWER SECONDARY VOLTAGE FUSE
VA 12 -0 – 12 24 – 0 – 24 55 – 0 – 55 110 – 0 – 110 Standard type
50 2 1 0.4 0.2 ICE 127 CF
100 4 2 0.8 0.4
150 6.3 3.15 1.25 0.63
200 8 4 1.6 1.25
300 12 6.3 2.5 1.6
400 16 8 3.15 2
500 20 10 4 3.15
750 32 16 6.3 4
1000 40 20 8 6
1250 50 25 10 6
1500 63 32 12 8
2000 80 40 16 10
2500 20
3000 25
3500 tension>25A tension>25A
4000 IEC 269 GL
5000

Protection of the primary circuit. When the transformer is being connected, an excess current equivalent to approximately 25% In, will be calculated for at least 10 ms. The protection device is not to be interrupted during this initial working conditions. Therefore, and as the protection against overload is to be put on the secondary circuit, the primary one shall be protected against short-circuit risks only.

There are two possible type of protection devices:
– aM fuse in compliance with IEC 269
– C.m.c.b. fuse in compliance with IEC 898

The following table shows the protections to be applied for the primary circuit:

 

POWER PRIMARY 220V PRIMARY 220V PRIMARY 380V PRIMARY 380V
VA Fusible aM type C m.c.b. Fusible aM type C m.c.b.
50 1 1 1 1
100 1 3 1 2
150 1 6 1 2
200 1 6 1 3
300 1 10 2 6
400 4 10 2 6
500 6 16 4 10
750 8 16 4 10
1000 10 20 6 16
1250 10 25 8 20
1500 10 32 10 20
2000 12 40 10 25
2500 16 40 10 32
3000 16 50 12 40
3500 20 50 16 40
4000 20 63 16 50
5000 25 80 20 63

The aforementioned values are informative only and are to be used with transformers with an insertion tension equivalent to 25In

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