Page 11 - Application Guide Semiconductor Fuse Link

real-world working conditions

Example 1

A 900A fuse has the following data, which is given in published literature :

a = 130 °C o = 30 °C C1 = 0.85 B1 = 1.25

What is the maximum allowable continuous current for the fuse under the following conditions
of use?

ambient temperature = 55 °C forced air cooling with v = 2 m/s
frequency = 1000 Hz continuous operation with one overnight stop per day

130 - 55
-
A1 = 130 - 30 Bv = 1 + (B1 -1) * (2/5) = 1.1

From Table 1, CPE = 0.90 and from Table 2, A’2 = 0.90. The adjusted rating is then

In’ = In x A1 x Bv x C1 x CPE x A’2

In’ = 900 x 0.866 x 1.1 x 0.85 x 0.90 x 0.90 = 590.3A

Note that this is considerably lower than the nominal value.

These coeffi cients are used for routine applications. For unusual applications a more detailed study
of thermal, high frequency, and other effects may be required. Contact Ferraz Shawmut Technical
Services for guidance.

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