Voltage and temperature derating due to altitude
Certain conditions should be considered when choosing an installation location at high altitudes. Air pressure
decreases as altitude above sea level increases. The reduced air density results in less effective heat dispersal,
hence the need to reduce rated operating temperatures. The dielectric strength of air also drops as the air pressure
drops, necessitating a reduction in rated operating voltages so to avoid electric arcs in high voltage circuits.
Standard design guidelines cover normal operation up to 6,600 feet (2,000 meters) elevation. Guidelines provided
below will aid the designer in planning installations above 6,600 feet. These are not invariable rules, rather
guidelines to aid the designer.
Temperature derating
The Y-axis of the graph below is the normalized temperature derating. The inverter’s rated maximum ambient
temperature applies up to altitudes of 6,600 feet (2,000 meters). Between 6,600 and 10,000 feet, the ambient
temperature for the inverter must be decreased by the corresponding fraction shown on the Y-axis of the graph.
These derating guidelines are applicable to both indoor and outdoor applications.The system designer should
consider the site layout, wind, typical maximum temperatures, and other environmental parameters in determining
whether less derating is acceptable. Examples of altitude derating calculation can be found on the next page.
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1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000
Normalized temperature (Tmax derated / Tmax sea level)
Altitude (feet and meters)
Altitude vs normalized working temperature
3280 3937 4593 5249 5905 6561 7217 7874 8530 9186 9842
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