Accessories, The external transformer is required for the earth-fault protection., a) For the neutral conductor in the case of 3-pole circuit-breakers, b) For directly measuring the ground fault current at the grounded neutral point in the case of 3-pole and 4-pole circuit-breakers., Pole 3, For use with IZMX-DTV-G, +IZMX-DTV-G, +IZMX-DTV-GZ, +IZMX-DTU-A, IZMX-DTU-A, +IZMX-DTU-AZ, +IZMX-DTU-G, IZMX-DTU-G, +IZMX-DTU-AM, IZMX-DTU-AM, +IZMX-DTU-AMZ, IZMX-DTU-GMZ, IZMX-DTU-GM, +IZMX-DTU-GM, +IZMX-DTU-GZ, IZMX-DTP-G, IZMX-DTP-G, +IZMX-DTP-GZ, +IZMX-DTP-GM, +IZMX-DTP-GMZ, IZMX-DTP