DS215UCVAG3AD
故障回路不影响接地系统，基本上由相导体和保护导体串联而成。根据IEC 60364-4规定，为提供自动断开电路的保护，应满足以下条件：Zs·Ia≤ U0，其中：Zs是故障回路的阻抗，包括电源、故障点之前的带电导体以及故障点和电源之间的保护导体[Ω]; U0是标称交流r.m.s.接地电压【V】；I a是保护装置在表3中规定的时间内的断开电流（安培），作为电流不超过32A的终电路的额定电压U0的函数，或配电电路和电流超过32A的终电路在5秒内的函数（对于电路类型的描述，应参考TT系统给出的指示）.应通过适当协调断开时间和故障回路阻抗，选择自动装置，以防止相位PE故障和间接接触。在TN系统中，低压侧的螺栓故障相PE通常会产生类似于短路的电流，接地故障电流流经线路导体（或多个导体），而保护导体不会影响接地布置。Zs·Ia关系≤ U0可表示为：I a≤ U0=IkLPE Zs，其中IkLPE是相位PE故障电流。因此，可以说明，当保护装置的跳闸电流I a（在表3所示时间内或5s内）低于待保护外露导电部分的相PE故障电流IkLPE时，可验证间接接触保护。在TN系统中，以下装置用于防止间接接触：•带热磁脱扣器的断路器；•带电子脱扣器的断路器剩余电流装置（仅TN-S）。

The fault loop does not affect the earthing system and is basically formed by the connection in series of the phase conductor and of the protective conductor. To provide a protection with automatic disconnection of the circuit, according to IEC 60364-4 prescriptions, the following condition shall be fulfilled: Zs · Ia ≤ U0 where: Zs is the impedance of the fault loop comprising the source, the live conductor up to the point of the fault and the protective conductor between the point of the fault and the source [Ω]; U0 is the nominal ac r.m.s. voltage to earth [V]; I a is the disconnection current in amperes of the protective device within the times defined in Table 3 as a function of the rated voltage U0 for final circuits with currents not exceeding 32A or within 5 seconds for distribution circuits and for final circuits with current exceeding 32A (for a description of the circuit typologies reference shall be made to the indications given for TT systems).The choice of the automatic device for the protection against phase-PE faults and against indirect contact shall be carried out by coordinating properly the disconnection times with the impedance of the fault loop. In TN systems a bolted fault phase-PE on the LV side usually generates a current similar to that of a short-circuit and the earth fault current flowing through the line conductor (or conductors) and the protective conductor does not absolutely affect the earthing arrangement. The relationship Zs · Ia ≤ U0 may be expressed as: I a ≤ U0 = IkLPE Zs where IkLPE is the phase-PE fault current. Therefore, it is possible to state that the protection against indirect contact is verified when the tripping current I a of the protective device (within the times shown in Table 3 or within 5s) is lower than the phase-PE fault current IkLPE at the exposed-conductive-part to be protected. In TN systems the following devices are used for protection against indirect contact: • circuit-breakers with thermomagnetic releases; • circuit-breakers with electronic releases; • residual current devices (TN-S only).