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为了在TN系统中防止用电人员接触到在电气设备发生接地故障时带电的外露可导电部分而发生危险,在强制性国家标准GB 16895.21—2004《建筑物电气装置第4-41部分:安全防护电击防护》中,对此类故障规定了间接接触防护措施。其中,最常用的措施就是自动切断电源。第413.1.3.3条中规定:TN系统中当装置内任何地方发生相导体与保护导体或外露可导电部分之间阻抗可忽略的故障时,保护电器的特性和回路阻抗应使其在规定的时间内自动切断电源,下式可满足。
In the TN system to prevent electrical personnel exposed to electrical equipment in the event of a grounding fault live exposed conductive part of the dangerous, mandatory national standard GB 16895.21-2004 “Building Electrical Installations Part 4-41: Security Shock protection ”, provides for indirect contact protection measures for such failures. Among them, the most commonly used measure is automatically cut off the power. Article 413.1.3.3 states: When a fault occurs in a TN system where the impedance between the phase conductor and the protective conductor or the exposed conductive part occurs negligibly within the device, the characteristics of the protective device and the impedance of the circuit shall be such that, at a specified time Automatically cut off the power, the following formula can be met.