Applications
3.4 Use of 3VA UL molded case circuit breaker in DC systems
3VA molded case circuit breakers with UL and IEC certification
142 Manual, 01/2019, L1V30435333-01
The same thermal-magnetic trip units used as line protection devices in AC installations are
also available for protecting DC installations.
However, a correction factor must be applied to the magnetic trip unit, relative to the actual
current rating.
Example:
3VA51 100 A, TM230 FTAM:
If the switching device is to trip instantaneously on an overcurrent of 1000 A, the parameter I
i
for instantaneous short-circuit current protection (I) is set to:
I
i
= 1000 A x 0.7 = 700 A.
For further information on trip units and details about the setting parameters, please refer to
chapter Applications in line protection (Page 99).
It is not possible to use electronic trip units for this application.
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