Friend of Human being

               Earth Leakage relay (ELR) used to protect human being from electrical shock. It is a big brother of ELCB which is use in household. Earth leakage relay has input from CBCT(Core balance current transformer), Auxiliary supply 230V AC and NO, NC contacts.

              In CBCT, When three phase are balanced then in secondary side no current flows but when any phase draw more current then other two phases which is generally earth fault condition then it will give trip command to MCCB or Contactor. If you are using ELR in simple feeder then you need to use 3.5 core cable 3 phase+1 neutral and all need to pass from CBCT so it will not give tripping im unbalance condition. But if you are using ELR in motor then you need to use 3 core cable and all phases need to pass from CBCT.

                When you need to cut supply from MCCB then you need to use NO contact and when you need to motor off then use NC contact in series with contactor coil.

            In picture, electromechanical type elr is shown. it is rare. It has only one NC contact so you can use this ELR in only motor which run through contactors.

            Nowadays many electronic ELR is available which has current setting as well as time setting so you can adjust it from your requirement.