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What is the meaning of trip class ( like class 10 ) in LRD overload relays.

The creation of thermal tripping classes allows better adaptation of the thermal protection to suit different motor
and application technologies (short or long starting times). 
Conforming to IEC 60947-4-1 and IEC 60947-6-2, the meaning of the tripping class is that the relay will trip in how
much time at 7.2 times of rated current.
Class                              10A             10             20           30
Tripping time at 7.2Ir    2…10 s     4…10 s      6…20 s     9…30 s

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