Derating
￭ Surrounding air temperature derating
In the temperature range +40…50 °C (+104…122 °F), the rated output current is derated
by 1 percentage point for every added 1 °C (1.8 °F). The output current can be calculated
by multiplying the current given in the rating table by the derating factor (k):
T
1.00
0.90
+40 °C
+104 °F
+50 °C
+122 °F
k
0.80
￭ Altitude derating
At altitudes 1000 … 2000 m (3281 … 6562 ft) above sea level, the output current derating
is 1 percentage point for every added 100 m (328 ft). For example, the derating factor for
1500 m (4921 ft) is 0.95. For altitudes above 2000 m (6562 ft), contact ABB.
If surrounding air temperature is below +40 °C, the derating can be reduced by 1.5
percentage points for every 1 °C reduction in temperature. A few altitude derating curves
are shown below.
Technical data 135
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