Current-Carrying Capacity And Operating Temperature - Mitsubishi Electric C Series Handling And Maintenance

3.6.6 Current-carrying capacity and operating temperature

(1) Operating current vs. ambient temperature
Rated current of circuit breakers is adjusted for the rated ambient temperature. This is because circuit
breakers are often installed in a casing as a switchboard or a control board, and temperature of the
installed place of the breaker becomes higher than ambient temperature of the wires. If temperature of
the installation site of circuit breakers greatly differ from the rated ambient temperature, it is necessary
to correct rated current according to the temperature correction curve (shown in the Paragraph of
characteristics and outside shape in the catalog). Load current can be increased up to the rated cur-
rent corrected according to ambient temperature.
However, set current rating with enough allowance while taking fluctuation of power voltage and load
current into consideration so that maximum operating current may not exceed the rated current.
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