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21.1.1 The spacings through air and over surface in an appliance shall not be less than 1/16 inch (1.6: O v$ o$ Z- D/ V$ N: f
mm) between uninsulated live parts of opposite polarity; and between a rigidly mounted uninsulated live
8 m. ~. @6 o3 {' v6 _, Wpart and a dead metal part that either is exposed for persons to contact or may be grounded.
2 M' _: {" ]; H. M1 jException No. 1: If exact centering of the cold pin of a sheathed-type heating element is required to/ i; C" ^0 r5 W: j* C% @
maintain the 1/16 inch (1.6 mm) spacing, a spacing of 3/64 inch (1.2 mm) in one location is acceptable.
1 `- d' k) p# D* Z4 \+ hException No. 2: Spacings in an appliance that comply with 21.1.2 need not comply with 21.1.1.
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% o) ^' g9 G5 ^/ i6 u& ~ v21.1.2 At closed-in points only, such as the screw-and-washer construction of an insulated terminal* u, c- b1 R. q% Y
mounted in metal, a spacing of 3/64 inch (1.2 mm) is acceptable. Within a thermostat, except at contacts,
5 J6 i2 `8 O, b* `9 } T5 \% Vthe spacings between uninsulated live parts on opposite sides of the contacts shall not be less than 1/326 V- P' `0 s1 J8 Q, L
inch (0.8 mm) through air and 3/64 inch (1.2 mm) over the surface of insulating material, and the
8 [4 L z5 z6 I/ Oconstruction shall be such that the spacings are maintained permanently.8 n/ o; h8 @ P$ ?; H& v1 y
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a. 21.1.1 中例外1,发热管里面有发热丝然后通过焊接一段延长出去（COLD PIN), 一般是圆柱体，EXACT centering 即COLD Pin 圆柱体中心，发热管有两端，意味着有两个cold pin, 这两个cold pin 圆柱体中心距离要求1.6mm, 后面说在一个位置可以有1.2mm 距离，什么叫一个位置(in one location)? 指的是那儿距离可以使1.2mm?
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b. 21.1.2, except at contacts, contacts这里是指温控器里面的触点吗？还是指温控器端子引脚？ 视乎是端子引脚对吧？ 也就是说端子引脚要有1.6mm 电气间隙和爬电距离。然后说温控器两端子引脚间电气连接暴露导体可以是0.8mm 间隙，1.2mm 爬电？对吗？ 什么样的结构是认为maintained permanently?- R& B' R3 M1 j
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