Derating For The Electronic Trip Units Of 3Va6 Molded Case Circuit Breakers - Siemens Sentron 3VA Manual

Technical specifications
6.4 Derating
Example
Starting point:
A 3VA5 200 A molded case circuit breaker with a TM230 trip unit is used in a
400 Hz application. The molded case circuit breaker is to trip instantaneously at an
overcurrent of 2000 A.
The maximum permissible rated continuous operational current is calculated first:
200 A · 0.9 = 180 A
The setting value for instantaneous short-circuit protection (I
basis of the correction factor from the table above:
I = 2000 A · 0.6 = 1200 A
i
6.4.4

Derating for the electronic trip units of 3VA6 molded case circuit breakers

The ambient temperature has no effect on the current measurement of the electronic trip
units of 3VA6 molded case circuit breakers. 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 contain 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
The 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).
When connecting terminals with control wire tap are used, the total current from the main
circuit and control wire must not exceed the maximum rated operational current of the
molded case circuit breaker.
458
) is then determined on the
i
3VA molded case circuit breakers with UL and IEC certification
Manual, 01/2019, L1V30435333-01