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各个IEC电源保护分类有何区别?

2020年8月4日作者 Bruce Rose - 4分钟阅读

各个IEC电源保护分类有何区别?

国际电工委员会(IEC)定义了三种电源安全分类:I类、II类和III类。These three classes are used to identify different methods for preventing the user of the power supply from being subjected to hazardous voltages from the input power source. Although it is easy to understand the differences in the IEC classes, many engineers are not familiar with the definitions and thus this blog will present a quick explanation of the differences between the classes.

  1. Class I - a layer of basic insulation and a grounded conductive chassis
  2. Class II - double insulation (basic + supplemental) or reinforced insulation
  3. Class III - no protection needed as the input voltage is not hazardous

Class I Power Supplies

In IEC Class I power supplies the user is protected from hazardous input voltage levels by at least a layer of basic insulation and a grounded conductive chassis. The first level of safety protection is provided by the basic insulation. The second level of safety protection is provided by the grounded conductive chassis. If there is a failure of the basic insulation, then any conductor with a hazardous voltage will be grounded by the conductive chassis before the hazardous voltage can come in contact with the user. All Class I power supplies must have safety ground brought to an electrically conductive chassis in the power supply.

Diagram of Class I power supply requirements

Class II Power Supplies

In IEC Class II power supplies the user is protected from hazardous input voltage levels by at least a layer of basic insulation and a layer of supplemental insulation or a layer of reinforced insulation. For double insulation, the first level of safety protection is provided by the basic insulation while the second level of safety protection is provided by the layer of supplemental insulation. Reinforced insulation provides the same safety factor as the combined basic and supplemental layers of insulation but in a single layer of insulation. For more on insulation check out our blog post on Insulation, Isolation, and Working Voltage.

Because of double or reinforced insulation, IEC Class II power supplies are not required to have the safety ground conductor brought to the power supply.

Diagram of Class II power supply requirements

A common source of confusion is the difference between an IEC Class II power supply and a NEC Class 2 power supply. This topic is covered in our post What's the Difference Between Class 2 and Class II Power Supplies?

Class III Power Supplies

In IEC Class III power supplies the input voltage is not at a hazardous level and thus the user does not need to be protected from the input voltage. The IEC label for the non-hazardous input voltage is Safety Extra Low Voltage (SELV). The voltage in accessible parts of SELV circuits shall not exceed 42.4 Vac peak or 60 Vdc for longer than 200 ms., with an absolute limit of 71 Vac peak or 120 Vdc. SELV circuits must be separated from hazardous voltages by two levels of protection. The two layers of protection may be basic and supplemental insulation, reinforced insulation, or basic insulation combined with a safety grounded electrically conductive chassis.

Diagram of Class III power supply requirements

Understanding the three IEC Power Supply Protection Classes enables those specifying or selecting power supplies to choose the appropriate class of supply based upon safety, regulatory, and cost constraints.

类别: 基础知识产品选择

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Bruce Rose

Bruce Rose

首席应用设计师

Bruce Rose在电子产品行业从事多年设计、销售和营销工作,主要致力于模拟电路和功率输送领域。他的工作经验涉及组织和主持国际研讨会、在超过40个技术大会和期刊中出版文章和发表演讲,并且获得了七项专利。Bruce不仅享受工作,更加享受与家人共度远足、骑行和玩皮划艇的美妙时光,同时还热衷于各种规模和型号的航空器。

 
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