各位大俠:

有一問題請教:

關於UL STYLE 21491中的USE有說明以下內容,我想了解一下其中的Class 2是代表什麼意思?

謝謝啦!

USE   Internal or external wiring in class 2 circuits only

class 0/1/2/3 分别指的是设备类型，在这就表示这些设备中的用线。其分类如下：
  1 ) 0类设备是指靠基本绝缘作为触电防护设备。这些设备一旦基本绝缘失效，设备的安全性取决于用电环境。由于0类设备的触电防护条件较差，在一些工业发达国家已逐渐禁止生产这类设备。
  2) 1类设备是指触电防护不仅靠基本绝缘，还需将外漏可导部分与设施固定布线的保护线相联接的设备，也就是说需要采用保护接地或保护接零的设备。
  3) 2类设备是指具有加强绝缘或双重绝缘的设备，这类设备的外壳一般不得与保护线相连。
  4) 3类设备是指靠安全特低电压供电的设备。
Please see explanation in English below：

［moveitgogo 在 2010-6-2 21:52:32 编辑过］

［moveitgogo 在 2010-6-2 21:53:04 编辑过］

1）class 0: These appliances have no protective-earth connection and feature only a single level of insulation and were intended for use in dry areas. In most countries, the sale of Class 0 mains-voltage appliances is prohibited today, as a single fault could cause an electric shock or other dangerous occurrence. The International Electrotechnical Commission is in the process of removing provisions for Class 0 devices from its standards. It can be expected that the Class 0 concept will eventually disappear from the international market, in favour of Class II devices。

2) class 1:These appliances must have their chassis connected to electrical earth (US: ground) by an earth conductor (coloured yellow/green in most countries, green in the U.S., Canada and Japan). A fault in the appliance which causes a live conductor to contact the casing will cause a current to flow in the earth conductor. This current should trip either an overcurrent device (fuse or circuit breaker) or a residual current circuit breaker (ground fault circuit interrupter [GFCI]) which will cut off the supply of electricity to the appliance.

3) class 2:A Class II or double insulated electrical appliance is one which has been designed in such a way that it does not require a safety connection to electrical earth (US: ground).The basic requirement is that no single failure can result in dangerous voltage becoming exposed so that it might cause an electric shock and that this is achieved without relying on an earthed metal casing. This is usually achieved at least in part by having two layers of insulating material surrounding live parts or by using reinforced insulation.In Europe, a double insulated appliance must be labelled "Class II", "double insulated" or bear the double insulation symbol (a square inside another square).

4)class 3:A Class III appliance is designed to be supplied from a SELV (Separated or Safety Extra-Low Voltage) power source. The voltage from a SELV supply is low enough that under normal conditions a person can safely come into contact with it without risk of electrical shock. The extra safety features built into Class I and Class II appliances are therefore not required. For medical devices compliance with Class III is not considered sufficient protection .

謝了,樓上的大俠 !

我還有點質疑:

針對UL在STYLE PAGE上要求這些不同的設備類型,在電線設計上要做哪些區分呢?

在結構上是否要注意些什麼?

此Class 2非彼Class II，一般来讲，UL的Class 2的概念是指通过变压器隔离的低压回路。

電線就參考UL758, UL1581而已