Siemens SENTRON 3VA1 Manual page 638

Technical specifications
6.4 Derating and temperature compensation
The table below shows the correction factors of setting value I
molded case circuit breakers in plug-in / draw-out technology and for 3VA1 molded case
circuit breakers combined with residual current devices:
Example
Starting point:
The current loading of a 3VA1 molded case circuit breaker is calculated to be 90 A and the
ambient temperature 65 °C for a given application. The plug-in version of the molded case
circuit breaker will be used.
The appropriate size of molded case circuit breaker is determined first on the basis of the
correction factor for 3VA1 plug-in technology (see table above):
Design of assembly at 50 °C: I
It is therefore necessary to select a molded case circuit breaker that allows a setting value of
100 A on the thermal overload release at a calibration temperature of 50 °C. A 3VA1 molded
case circuit breaker 160 A with I
The temperature compensation is then calculated according to the method described above:
● Ambient temperature 65 °C:
Setting factor EF(50 °C) = (100 / 125) = 0.8
Correction factor K = 0.69 (from chart)
Switching device temperature compensation TK(65 °C) = (0.69 · (65 °C ... 50 °C) /
100) + 1 = 1.1
Setting value I
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).
636
= (90 A / 0.9) = 100 A
r
= 125 A is therefore used for the application.
n
= 125 A · 0.9 · 1.1 = 124 A
r(65 °C)
for the trip units of 3VA1
r
3VA molded case circuit breakers with IEC certificate
Manual, 03/2019, A5E03603177010-03