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在以下情況下，可確保防止直接和間接接觸：
符合IEC 60364-4-41第411條規(guī)定的要求；尤其：
-額定電壓不得超過(guò)50 V ac r.m.s.和120 V無(wú)紋波直流；
-電源應(yīng)為SELV或PELV電源；
-為此類(lèi)電路提供的所有安裝條件應(yīng)
得到滿(mǎn)足。
SELV電路具有以下特征：
1） 它由獨(dú)立電源或安全電源供電。獨(dú)立的
電源為電池或柴油發(fā)電機(jī)。安全源是供應(yīng)品
通過(guò)隔離變壓器獲得；
2） 沒(méi)有接地點(diǎn)。兩個(gè)外露導(dǎo)電電纜的接地
禁止使用SELV電路的部件和帶電部件；
3） 它應(yīng)與其他電氣系統(tǒng)分開(kāi)。SELV的分離
所有部件應(yīng)保證來(lái)自其他電路的系統(tǒng)；對(duì)于
為此，SELV電路的導(dǎo)體可以包含在多芯電纜中，或者可以配備額外的絕緣護(hù)套。
PELV電路具有與SELV系統(tǒng)相同的規(guī)定，除了
禁止接地點(diǎn)；事實(shí)上，在骨盆回路中，至少有一個(gè)點(diǎn)是
始終接地。
ABB |電氣設(shè)備447
4保護(hù)人類(lèi)
4.3直接和間接接觸防護(hù)
1SDC010043F0201
沒(méi)有安全源，
接地連接
是可以接受的
安全隔離變壓器
或等效源，
接地連接
是可以接受的
L1
L2
L3級(jí)
N
SELV公司
安全隔離
變壓器
或同等產(chǎn)品
來(lái)源
無(wú)接地
骨盆FELV
PELV電路FELV電路
體育課
E
體育課
E
II類(lèi)
設(shè)備
電壓限制
超低電壓：
50伏交流電
120 V dc
隔層導(dǎo)電部件的接地連接，
e、 g.通過(guò)金屬管或鋼結(jié)構(gòu)工程
保護(hù)導(dǎo)體
接地電極
體育課
E
體育課
注1：本圖中未顯示過(guò)電流保護(hù)裝置。
當(dāng)出于功能原因要求SELV或
PELV電路無(wú)法實(shí)現(xiàn)；他們需要遵守以下規(guī)則：
a） 應(yīng)通過(guò)以下方式提供直接接觸保護(hù)：
-防護(hù)等級(jí)符合以下要求的屏障或外殼：
上述（防止直接接觸的措施）；
-與規(guī)定的小試驗(yàn)電壓相對(duì)應(yīng)的絕緣
一次電路。如果未通過(guò)該測(cè)試，則應(yīng)在安裝過(guò)程中加強(qiáng)設(shè)備可觸及非導(dǎo)電部件的絕緣，以便
能夠承受1500 V ac r.m.s.的試驗(yàn)電壓1分鐘。；

The protection against both direct and indirect contact is ensured if the requirements stated in 411 from IEC 60364-4-41 are fulfilled; particularly: - the rated voltage shall not exceeds 50 V ac r.m.s. and 120 V ripple-free dc; - the supply shall be a SELV or PELV source; - all the installation conditions provided for such types of electrical circuits shall be fulfilled. A SELV circuit has the following characteristics: 1) it is supplied by an independent source or by a safety source. Independent sources are batteries or diesel-driven generators. Safety sources are
supplies obtained through an isolating transformer; 2) there are no earthed points. The earthing of both the exposed conductive parts as well as of the live parts of a SELV circuit is forbidden; 3) it shall be separated from other electrical systems. The separation of a SELV system from other circuits shall be guaranteed for all the components; for this purpose, the conductors of the SELV circuit may be contained in multiconductor cables or may be provided with an additional insulating sheath. A PELV circuit has the same prescription of a SELV system, except for the prohibition of earthed points; in fact in PELV circuits, at least one point is always earthed. ABB | Electrical devices 447 4 Protection of human beings 4.3 Protection against both direct and indirect contact 1SDC010043F0201 no safety source, connection to earth is admissible safety isolating transformer or equivalent source, connection to earth is admissible L1 L2 L3 N SELV safety isolating transformer or equivalent source, no earthing PELV FELV PELV circuit FELV circuit PE E PE E Class II equipment voltage limits for extra-low voltages: 50 V ac 120 V dc earth connections by estraneous conductive parts, e.g. by metal pipe or structural steelwork protective conductor earth electrode PE E PE Note 1: Overcurrent protective devices are not shown in this figure. FELV circuits are used when for functional reasons the requirements for SELV or PELV circuits cannot be fulfilled; they require compliance with the following rules: a) protection against direct contact shall be provided by either: - barriers or enclosures with degree of protection in accordance with what stated above (measures of protection against direct contact); - insulation corresponding to the minimum test voltage specified for the primary circuit. If this test is not passed, the insulation of accessible nonconductive parts of the equipment shall be reinforced during erection so that it can withstand a test voltage of 1500 V ac r.m.s. for 1 min.;