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b） 應通過以下方式提供間接接觸保護：
-FELV設備外露導電部分的連接
連接至一次電路保護導體的電路，前提是
后者受一項防止直接
聯(lián)系
-將FELV電路的帶電導體連接到一次電路的保護導體，前提是自動斷開
電源用作保護措施；
c） FELV系統(tǒng)的插頭不得進入其他系統(tǒng)的插座
電壓系統(tǒng)和其他電壓系統(tǒng)的插頭不得
進入FELV系統(tǒng)的插座。
圖1顯示了SELV、PELV和FELV系統(tǒng)的主要特征。
圖1:SELV、PELV、FELV系統(tǒng)
448電氣設備| ABB
4保護人類
1SDC01035F0001
L1
L2
L3級
N
Ik
Ik
RB RA
4.4 TT系統(tǒng)
TT系統(tǒng)中的接地故障涉及圖1所示的電路：
圖1:TT系統(tǒng)中的接地故障
故障電流流經(jīng)變壓器的二次繞組
線路導體、故障電阻、保護導體和接地
電極電阻（用戶工廠的RA和中性點的RB）。
根據(jù)IEC 60364-4規(guī)定，保護裝置必須與接地裝置協(xié)調(diào)，以快速斷開電源
如果接觸電壓達到對人體有害的值。

b) protection against indirect contact shall be provided by: - connection of the exposed conductive parts of the equipment of the FELV circuit to the protective conductor of the primary circuit, provided that the latter is subject to one of the measures of protection against direct contact; - connection of a live conductor of the FELV circuit to the protective conductor of the primary circuit provided that an automatic disconnection of the supply is applied as measure of protection; c) plugs of FELV systems shall not be able to enter socket-outlets of other voltage systems, and plugs of other voltage systems shall not be able to enter socket-outlets of FELV systems. Figure 1 shows the main features of SELV, PELV and FELV systems. Figure 1: SELV, PELV, FELV systems 448 Electrical devices | ABB 4 Protection of human beings 1SDC010035F0001 L1 L2 L3 N Ik Ik RB RA 4.4 TT System An earth fault in a TT system involves the circuit represented in Figure 1: Figure 1: Earth fault in TT system The fault current flows through the secondary winding of the transformer, the line conductor, the fault resistance, the protective conductor, and the earth electrode resistances (RA, of the user’s plant, and RB, of the neutral). According to IEC 60364-4 prescriptions, the protective devices must be coordinated with the earthing arrangement in order to rapidly disconnect the supply if the touch voltage reaches harmful values for the human body.