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Variants

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.

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Example:

3VA1 160 A, TM240 ATAM:
If the switching device is to trip instantaneously in response to an overcurrent of 1200 A, the parameter Ii for instantaneous short-circuit protection (I) must be set to:

Ii = 1200 A x 0.7 = 840 A.

For further information on trip units and details about setting parameters, please refer to chapter "Line protection applications of 3VA molded case circuit breakers".

It is not possible to use electronic trip units for this application.