Overload relay current setting:
Overload relay is used to protect an electrical motor from over current (thermal protection). When the motor current is more than the current setting in the relay, the relay just open the motor circuit to avoid further flow of current. The overloads relay current setting will be varied between the DOL, Star-Delta, auto transformer, Rotor resistance starter and the VFD with Starter to starter.
DOL Starter is nothing but a direct online starter, in which the motor will be connected direct to the motor. Hence the full current shall be applied to the motor.
Overload Relay setting = 100% of the full load current.
Star delta starter:
Star delta starter’s overload current setting is equal to the 0.58 times of the full load current while placing the relay @ the output of the main contactor.
Overload relay setting = 0.58 x FLA (Full Load Amps)
Auto Transformer starter:
Auto transformer starter’s OLR relay will be connected in two models. One is single contactor logic and another one is double contactor logic.
For single contactor logic, the relay setting will be 100% of the motor’s full load current. But for the double contactor logic, the relay can be designed for 1/1.732 times of the full load current.
Hence our recommendation is to use double contactor logic and it is very cost effective.
Auto transformer relay setting = FLA / 1.732.