Page 45 - Application Guide Semiconductor Fuse Link

Appendix

(a) summary of coeffi cients used in fuse selection

To allow for : Coeffi cient Notes

ambient temperature A1 where a = ambient.
a - o
-
a = 130-150 ºC. o = 25-30 ºC.
A1 = a - o
(See section 5).

forced cooling Bv Increases linearly from 1.0 to B1 at v = 5m/s then
constant. Typically B1 = 1.25.
(See section 5).

cable/bus size C1 To allow for the fact that in service the cooling
effect of the connections (cables, busbars) will
normally be less favorable than was used in the type

tests used for establishing the current rating.
(See section 5 and Appendix b).
proximity & skin effect CPE To allow for proximity and skin effects at high
frequencies.
(See section 5).

fl uctuations in load current A’2 To allow for variations in r.m.s. current - see section 2.
Consult Ferraz Shawmut for cyclic loads.
(See section 5).

repetitive cyclic overloads B’2 Ratio of the maximum repetitive overload current to

the melting current, to ensure that the fuse will endure
a given number of cycles. (See section 6).

occasional overload Cf3 Ratio of the maximum occasional overload current,
in relation to the melting current, to ensure that the
fuse will survive without adverse effects.
(See section 7).

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