The DER3/0D or the earth differential relay is mainly used on LV networks in an alternative current of type TT and TN. It has a broad adjustment of threshold current dispersion and threshold for delay intervention. The device is designed in accordance with strict regulations. With this design, it meet the expectation to have a double need which are the safety of facility and the continuous service of industrial production. The relay consist of one intervention threshold, a control of opening coil and an auto-diagnostic made by led.