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Technical Advice
Influence of ambient
temperature (cont.)
Maximum permissible current
b
b
The maximum current allowed to flow through the device depends on the ambient
temperature in which it is placed.
b
b
The ambient temperature is the temperature inside the enclosure or switchboard
in which the devices are installed.
b
b
The reference temperature is in a halftone colour for the different devices.
b
b
When several devices operating simultaneously are mounted side by side in a
small enclosure, a temperature rise in the enclosure results in a reduction in the
operating current. A reduction coefficient of 0.8 will then have to be assigned to the
rating (already derated, if applicable, depending on the ambient temperature).
b
b
Example:
Depending on the ambient temperature and the method of installation, the table
below shows how to determine, for an iC60, the operating currents not to be
exceeded for ratings 25 A, 32 A and 40 A (reference temperature 50°C).
Operating current not to be exceeded (A)
Installation
conditions (IEC
60947-2)
iC60 alone
Several iC60 in the same enclosure
(calculate with the reduction coefficient
indicated below)
Ambient
temperature (°C)
35°C 50°C 65°C 35°C
50°C
65°C
Type Nominal
rating (A)
Actual rating (A)
iC60 25
26.35 25 23.57 26.35 x 0.8 = 21 25 x 0.8 = 20 23.57 x 0.8 = 19
32
34 32 29.9 34 x 0.8 = 27 32 x 0.8 = 25.6 29.9 x 0.8 = 24
40
42.5 40 37.34 42.5 x 0.8 = 34 40 x 0.8 = 32 37.34 x 0.8 = 30