I need a relay whose o/p must be like change from NC to NO under a single i/p to the contactor.

 

Latching relay...but...what and when will change it back to NC?

Ken

 

Check out the PDF link here: http://www.datasheetarchive.com/AZ850P1-3-datasheet.html

It is a Bi-Stable relay. Pulse coil one polarity and it switches---Pulse coil opposite polarity and it returns.
Last polarity on coil determines what is considered NO or NC contact.