Since there is a reduced cooling effect at high altitudes, the continuous current rating of a fuse will need to be derated for applications above 2000m. The following equation can be used to determine the adjusted current rating:
IA = I * XA
XA = 1 – (A – 2000)/20000
IA = Altitude Adjusted Current Rating of the Fuse
I = Current Rating of the Fuse
A = Altitude of the Application
XA = Altitude Derating Factor
Example
For a 30A fuse at 3000m
XA = 1 - (3000-2000)/20000 = 1 – 0.05 = 0.95
IA = 30 * 0.95 = 28.5A
Source - Littelfuse: Altitude Derating
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