Technical specifications
6.4 Derating and temperature compensation
3VA molded case circuit breakers
Manual, 04/2015, A5E03603177010-02
493
The operational current must never exceed the maximum rated operational current I
n
of the
molded case circuit breaker. If the current calculated for the operating conditions is higher
than the rated operational current of the unit, a molded case circuit breaker with the
appropriate rated operational current must be deployed.
Example 1: Correction of setting values as a function of ambient temperature
Starting point:
On a 3VA1 100 A molded case circuit breaker with a TM240 100 A trip unit, the real tripping
threshold for various different service temperatures must be set to a required system current
of I = 90 A.
●
Ambient temperature 60 °C:
Setting factor EF(50 °C) = (90 / 100) = 0.9
Correction factor K = 0.58 (see chart above)
Temperature compensation TK(60 °C) = (0.58 · (60 °C - 50 °C) / 100) + 1 = 1.058
Setting value I
r(60 °C)
= 100 A · 0.9 · 1.058 = 95 A
●
Ambient temperature 40 °C:
Setting factor EF(50 °C) = (90 / 100) = 0.9
Correction factor K = 0.58
Temperature compensation TK(40 °C) = (0.58 · (40 °C - 50 °C) / 100) + 1 = 0.942
Setting value I
r(40 °C)
= 100 A · 0.9 · 0.942 = 85 A
If the setting value calculated for the thermal trip unit I
r(TU)
is outside the possible setting
range, an appropriate molded case circuit breaker with a higher or lower rated operational
current must be selected and the compensation calculation then performed again.
Note
These values do not apply to all mounting conditions for molded case circuit breakers 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).
Summary of Contents for 3VA1 100 A
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