在以下情况下，可确保防止直接和间接接触：
符合IEC 60364-4-41第411条规定的要求；尤其：
-额定电压不得超过50 V ac r.m.s.和120 V无纹波直流；
-电源应为SELV或PELV电源；
-为此类电路提供的所有安装条件应
得到满足。
SELV电路具有以下特征：
1） 它由独立电源或安全电源供电。独立的
电源为电池或柴油发电机。安全源是供应品
通过隔离变压器获得；
2） 没有接地点。两个外露导电电缆的接地
禁止使用SELV电路的部件和带电部件；
3） 它应与其他电气系统分开。SELV的分离
所有部件应保证来自其他电路的系统；对于
为此，SELV电路的导体可以包含在多芯电缆中，或者可以配备额外的绝缘护套。
PELV电路具有与SELV系统相同的规定，除了
禁止接地点；事实上，在骨盆回路中，至少有一个点是
始终接地。
ABB |电气设备447
4保护人类
4.3直接和间接接触防护
1SDC010043F0201
没有安全源，
接地连接
是可以接受的
安全隔离变压器
或等效源，
接地连接
是可以接受的
L1
L2
L3级
N
SELV公司
安全隔离
变压器
或同等产品
来源
无接地
骨盆FELV
PELV电路FELV电路
体育课
E
体育课
E
II类
设备
电压限制
超低电压：
50伏交流电
120 V dc
隔层导电部件的接地连接，
e、 g.通过金属管或钢结构工程
保护导体
接地电极
体育课
E
体育课
注1：本图中未显示过电流保护装置。
当出于功能原因要求SELV或
PELV电路无法实现；他们需要遵守以下规则：
a） 应通过以下方式提供直接接触保护：
-防护等级符合以下要求的屏障或外壳：
上述（防止直接接触的措施）；
-与规定的小试验电压相对应的绝缘
一次电路。如果未通过该测试，则应在安装过程中加强设备可触及非导电部件的绝缘，以便
能够承受1500 V ac r.m.s.的试验电压1分钟。；

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.;