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6.4.6
Derating for the electronic trip units of 3VA2 molded case circuit breakers
The current measuring circuits of the electronic trip units of 3VA2 molded case circuit
breakers are not affected by the ambient temperature. The Rogowski coils integrated in the
trip unit measure the current and compare it to the set tripping threshold. Higher or lower
ambient temperatures do not influence the tripping threshold, which means that it is not
necessary to apply correction factors.
Limitation of the rated operational current
The temperature inside the molded case circuit breaker is nonetheless influenced by the
ambient temperature and the current-dependent power loss generated inside the unit. To
prevent overloading of molded case circuit breakers under difficult thermal conditions, the
maximum rated continuous operational current must therefore be limited as a function of the
ambient temperature in some cases:
The tables below specify the maximum rated uninterrupted operational current as a function
of the accessories to be taken into account and the ambient temperature. The operational
current must never exceed the maximum rated operational current of the molded case circuit
breaker.
Note
These values do not apply to all installation situations of the molded case circuit breaker and
may deviate depending upon factors such as cables and busbars, packing density,
ventilation, etc.
Please observe the applicable overriding guidelines (e.g. IEC 61439).
3VA molded case circuit breakers with IEC certificate
Manual, 03/2019, A5E03603177010-03
Technical specifications
6.4 Derating and temperature compensation
641
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