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High altitude derating factors for electrical systems

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Electrical power systems are affected by altitude. Standards indicate that an electrical device will operate satisfactorily at elevations between sea level and 1000 m. Per the IEEE document VOL. IA-20, NO. 2 a derate factor should be applied on equipment operated above 1000 m. 

Per the IEEE document VOL. IA-20, NO. 2 the derating factor for dielectric strength are unity from sea level to 1000 m, at which point the dielectric strength is derated at a rate of approximately one percent per 100 m /1000m ASL. (3% per 1000ft) 

Per Table Table III 

Altitude Derating Factor
1,000 m 1.00
1,500 m  .94
3,000 m  .82
4,000 m .78



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