What is TNC switch?

  • This is called TNC switch, It has three positions
  • Namely – Trip Neutral Close (TNC) switch
  • It is equipped with a spring so as to keep its terminal automatically in Neutral position after it is used for Closing or Tripping a Circuit Breaker either locally or remotely.
  • In any case, if the spring get damaged the circuit breaker (CB) may damage by the reason of “Hunting”, Hunting is nothing but the term that actually using for describing frequent ON-OFF-ON of CB.
  • Suppose a breaker is closed using TNC switch (Here, suppose spring of the switch is failed, it will not come to its Neutral position instead it maintain the same command CLOSED) and the same time it receives an open command as well to shunt coil either by the reason of overload or any fault condition, then because of this continuous open and close command the CB will damage eventually.

  • In order to avoid the CB failure under Hunting condition, we equipped CB with Anti pumping relay which is actually an Auxiliary relay.

Note : The breaker can be closed using Push button as well instead of TNC switch, ,so there is no need for Anti pumping relay.

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