Answer / rajesh t k

The NAT and NAC contacts are provided on TNC switch to facilitate additional functionalities from the TNC switch than mere Tripping or Closing.


These contacts are also known as Lost Motion Contacts. They help identify the last operation (Trip/Close) performed by the operator through the TNC switch.

The NAC contact will be closed whenever the operator turns the TNC lever to Close position and the contacts stays closed even after the lever is returned to the Neutral position by the operator, until the lever is turned to Trip side.

Hence, the 'Auto Trip' indication can be given via the NAC contact(instead of giving through an NO contact of the master trip relay), in series with the CB's 52b contact. That is, this is just an alternate way to wire up the 'Auto Trip' indication.

The NAT contact, likewise will be through whenever the CB has tripped via the TNC lever switch by the operator, until the lever is turned to Close position again.

Answer / k.prakashchandra

NAT- normal after trip and NAC normal after close.These are
'lost motion contacts' which indicate last operated position
of breaker .With NAC contact we get 'Auto-trip' indication
when the breaker is tripped by relay.

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