Our BY1-2+1-20 single-phase common-mode and differential-mode surge protectors are mainly used in spots where the network interference is rather serious. It can effectively restrict the peak pulse interference of the network and an inductive thunder current. It is mainly aimed at the overall protection of phase line and the zero line ground pointer required by a Ttand Tn-S electric-distribution system, and the common-mode and differential-mode when the phase line points to zero line. It is used as a precaution for level SPD C and SPD D.