PROBLEMSIEC 60364 - 4 – 41GB16895.21Protective equipotential bonding 保护等电位联结According to IEC61140 5.2.5 and IEC 60364-4-41 411.1, shall protective equipotential bonding be provided for outdoor TN and TT system with automatic disconnection of supply?根据IEC61140 （GB/T17045）5.2.5及IEC 60364-4-41 （GB16895.21）411.1，应为带有自动断电保护的户外TN和TT系统，提供保护等电位联结吗？What kind of earthing systems commonly used for external lightings (including street lighting) in foreign countries?在国外，外部照明（包括路灯）一般使用哪类接地系统？The permissible maximum disconnection time5 s or 1 s for circuits defined by IEC 60364-4-41 411.3.2.3and 411.3.2.4, in case of without protective equipotential bonding, can it ensure the protection against electric shock?IEC 60364-4-41（GB16895.21）411.3.2.3和411.3.2.4规定，允许最大断电时间5 s 或1 s，在没有保护等电位联结的情况下，能确保防电击吗？Wherever the steel reinforcement of concrete structures to be considered as external conductive parts, shall it be welded or it may be wrapped is allowable for protective equipotential bonding purpose? What about for down conductor of lightning protection system?将混凝土结构加强钢筋作为外部可导电部分考虑的任何情况下，应将其作为保护等电位联结进行焊接或缠绕吗？防雷系统的引下导体是怎样的？For building floors without steel reinforcement, shall it to be provided additional protective equipotential bonding? (e.g. mesh)没有钢筋的建筑楼层，应提供附加保护等电位联结吗？（比如：金属网）Fault loop impedance Z S 故障回路阻抗Z SFault loop impedance Z S of LV system is calculated by fundamental sequence impedance or by zero sequence impedance?低压系统的故障回路阻抗，是按基本阻抗还是按0区阻抗计算？TT system解释：根据IEC 60364-4-41（GB16895.21）411.5.1，由相同的保护电器予以保护所有外露导电部分，应通过保护导体连接至他们的公共接地极。
Clarify: In outdoor or wet locations, R A≤ U L./I D n, conventional touch voltage U L≤ 25 V. 澄清：户内或潮湿场所，R A≤ U L./I D n, 转换为接触电压U L≤ 25 V.IT systemExplain: Why isolation device shall be provided for neutral conductor of IT system with isolated neutral?解释：为何中性线隔离的IT系统，仍然要在中性线上安装隔离电器？What is the typical range of operating value of the insulation resistance for IMD? (several ten kΩor 0.5 MΩ)绝缘监测电器（IMD）的绝缘电阻的典型动作值范围是多少？（几十kΩ或0.5 MΩ）PELVWhere is PELV system commonly suitable (or not suitable) to be used?那些场合一般适合（或不适合）使用PELV？IEC 60364 – 4 – 42GB16895.2Protection against thermal effects 热效应保护Explanation: clause 422.3.9 for protection against fire.说明：422.3.9 条款是针对防火的规定：422.3.9 末端回路及用电设备应按以下要求进行绝缘故障保护a）在TN和TT系统中，应使用额定剩余动作电流IΔN≤300mA的RCDb）在IT系统中，应提供绝缘监测电器监测整个装置，或在末端回路中使用RCM。
做为选择，可使用a）中规定的额定剩余动作电流的RCD，在发生二次故障时予以断电保护。
Introduction on protection against fire risk that normally for public and office buildings and dwellings (including selection of cable types) in foreign countries.在防范火灾风险方面，请介绍一下国外对于公共建筑、办公建筑、住宅（包括线缆类型的选择）的一般情况。
IEC 60364 - 4 – 43GB16895.5Overload protection 过载保护Explain the factor 1.45 of formula I2≤ 1.45I Z, (regarding the tolerant of the characteristic curves, cyclic load or inrush current etc.)解释公式I2≤ 1.45I Z,中的系数1.45，（依据特性曲线的公差容限？周期性负荷？浪涌电流？等等）IEC 60364 - 4 – 44GB/T16895.16Earthing resistance R E 接地电阻R E1 HV neutral solid earthing and low resistance earthing1 高压中性点可靠接地与低阻接地- R E ≤2000 V/I E instead of R E ≤1200 V/I E (derived from IEC 60364-4-44:2007 Table 44.A1 and Table 44.A2);- R E ≤2000 V/I E代替R E ≤1200 V/I E（摘自IEC 60364-4-44:2007表44.A1及表44.A2）Note: The GB code considers the earth fault current of≥110 kV system can be ≥25 kA, in order to avoid R E too low, as well as the difficulties for separating the HV and LV earthing within the substation, in this case R E is allowed to be ≤ 5000 V/I E. (with provision of certain equipotential bonding and screening)注：GB考虑≥110 kV系统的接地故障电流可能≥25 kA，为避免R E过低，以及考虑到在变电站分隔高压与低压接地系统的困难，在这种情况下，接地电阻允许≤5000 V/I E.。
（带有某种等电位联结和屏蔽措施）Comment: As a result, the power frequency stress voltage U1 or U2 exceed the limit values defined by GB 16895.11(idt. IEC 60364-4-442:1993) and GB 61935.1(idt. IEC60664-1), the LV equipment may be damaged under earth fault situation.注释：其结果，源自U1或U2的电压，超过了GB 16895.11(idt. IEC 60364-4-442:1993) and GB 61935.1(idt. IEC60664-1)定义的限值，低压设备可能在接地故障时损坏。
What are the experiences and solutions concerning this problem in foreign countries? 国外在此问题上有何经验与解决方案？- The earthing of TN system is only allowed to be connected to the HV system R E .- TN系统的接地只允许连接至高压系统的R EComment: As a result, the implementation of TT and IT system are excluded, as well as the HV and LV earthing of TN system is not permitted to be separated.注释：其结果，TT和IT系统被排除在外，而且TN系统的高压与低压接地系统不允许被分隔2 HV neutral isolated or with resonance low or high resistance earthing2 高压中性点隔离或合理低阻或高阻接地- For power station and substation: R E ≤120 V/I E instead of R E ≤250 V/I E ..- For power grid supplying LV consumer: R E ≤ 50 V/I E .- 发电厂与变电站：R E ≤120 V/I E代替R E ≤250 V/I E …- 为低压用户供电的电网：R E ≤ 50 V/I EComment: Not necessary to reduce the value of R E under perfect protective equipotential bonding. 注释：在有可靠保护等电位联结的情况下不必降低R E值Some people consider that fault voltage U f and fault duration t may not be limited according to IEC 60364-4-44 Figure44.A2 in case of under perfect protective equipotential bonding.有些人认为，根据IEC 60364-4-44 （GB/T16895.16）图44.A2，在有可靠保护等电位联结的情况下，可不限制故障电压U f与故障持续时间t。