Technical specifications
6.4 Derating and temperature compensation
3VA molded case circuit breakers with IEC certificate
638
Manual, 03/2019, A5E03603177010-03
Example
Starting point:
A 3VA1 molded case circuit breaker 100 A with a TM240 trip unit is used for a 400 Hz
application. The molded case circuit breaker is required to trip instantaneously in response to
an overcurrent of 900 A.
The maximum permissible rated continuous operational current is calculated first:
100 A · 0.9 = 90 A
The setting value for instantaneous short-circuit protection (I
i
) is then determined on the
basis of the correction factor from the table above:
I
i
= 900 A · 0.7 = 630 A
6.4.4
Correction factors with direct current for the thermal-magnetic trip units of 3VA1
molded case circuit breakers
With DC systems, a correction factor must be applied to the magnetic trip unit.
Where ambient temperatures differ from the calibration temperature, temperature
compensation as described in chapter Derating of 3VA1 molded case circuit breakers
(Page 628) must be performed.
Example:
Starting point:
A 3VA1 molded case circuit breaker 160 A with a TM240 trip unit is used in a DC system.
The molded case circuit breaker is required to trip instantaneously in response to an
overcurrent of 1200 A.
The setting value for the instantaneous short-circuit protection (I
i
) is:
I
i
= 1200 A · 0.7 = 840 A
