零序电流保护一般适合使用于TN接地系统。因为当发生一相接地时，对TN-S系统Id回路阻抗包括相线阻抗Z1，PE线阻抗ZPE和接触阻抗Zf，Zs=Z1+ZPE+Zf;对于TN-C系统，Id回路阻抗包括相线阻抗Z1，PEN线阻抗ZPEN和接触电阻Zf，即ZS=Z1+ZPEN+Zf;对于TN-C-S系统，Id回路阻抗包括相线阻抗Z1，PEN线阻抗ZPEN，PE线阻抗ZPE和接触电阻Zf，即ZS=Z1+ZPEN+ZPE+Zf，产生的单相接地故障电流Id=220/ZS，明显大于无故障时的三相不平衡电流，只要整定合适，就可检测出发生接地故障时的零序电流，以切断故障回路。
Zero sequence current protection is generally suitable for TN grounding system. Because when one-phase grounding occurs, the Id loop impedance of TN-S system includes phase line impedance Z1, wufangbuc.07858.net tongdiaojd.71ix.comtongdiaoc.71ix.com tongdiaoj.71ix.comtongxianglu.71ix.comtongdiaoo.71ix.comPE line impedance ZPE and contact impedance Zf, Zs=Z1+ZPE+Zf; for TN-C system, Id loop impedance includes phase line impedance Z1, PEN line impedance ZPEN and contact resistance Zf, namely ZS=Z1+ZPEN+Zf; for TN-C-S system, Id loop impedance includes phase line impedance Z1, PEN line impedance ZPEN, line impedance Zf and contact resistance Zf. ZS = Z1 + ZPEN + ZPE + Zf, the single-phase grounding fault current Id = 220/ZS, is significantly larger than the three-phase unbalanced current when there is no fault. As long as the setting is appropriate, the zero-sequence current when the grounding fault occurs can be detected to cut off the fault circuit.
而对IT系统，一般均是使用对供电可靠性要求较高、对单相接地不必要立即切断供电回路、但需发出绝缘破坏监察信号、以维持继续供电一段时间的工矿企业内的不配出中性线的三相三线配电线路。
For IT systems, three-phase three-wire distribution lines without neutral lines are usually used, which require high reliability of power supply, do not need to cut off the power supply circuit immediately for single-phase grounding, but need to send out monitoring signals of insulation damage to maintain the non-distribution of neutral lines in industrial and mining enterprises for a period of time.