|
|
楼主 |
发表于 2011-8-21 22:36
|
显示全部楼层
RATIONALE:! S# _. p7 Z" V
6 n. \( F4 }" {$ A; B
Generally, when a fuse bursts it is because it is subjected to a short-circuit current that exceeds6 G) m B% \- q+ Q9 g9 d
the breaking (rupturing) capacity of the fuse. The informative Note to sub-clause 2.7.3
) k+ S6 C1 |# J) W. u3 G, x1 H(Short-circuit backup protection) states “If fuses complying with IEC 60127 are used in Primary
% q& ~4 ^; l4 f; w3 R; x6 g/ WCircuits, they should have high breaking capacity (1500 A) if the prospective short-circuit current8 d' i+ C+ A2 [4 ?) ]. M
exceeds 35 A or 10 times the rated current of the fuse, whichever is greater.” (In the U.S. and
) V) `# d7 ^ g5 B& ~4 B9 tCanada, UL 248-14 fuses are indicated as appropriate alternative fuses per Annex P.2, and thus" y; _" g1 i6 |$ F
a similar consideration applies.) Typically, high breaking fuses are ceramic, not glass cased, and
& J( V% N8 [7 n4 P1 V8 Athe note is attempting to document that the breaking capacity of a fuse is a valid consideration
3 x1 K1 S7 N/ aduring performance testing.& A8 B0 B3 B5 v: |1 |' t
+ t# s& N0 B& H. ]. i
Furthermore, a bursting fuse can expel dead metal parts onto surrounding circuitry, potentially
1 G& A f$ H7 {8 l" |bridging insulation and contributing to risk of fire or electric shock. Similarly, glass and metal
/ R7 o8 n/ |) t7 lpieces can be expelled through nearby enclosure openings.9 c( l2 K" H; r
0 x/ a. Y9 Q& v+ T& J" e
Also, a bursting fuse terminating a test also is not a consistently repeatable result - during one- d" t: k/ Z% { p7 h- i* R- C0 C
application of a fault, the fuse may burst but none of the glass or metal may exit the unit or; B6 ~; Q2 J* b: e Q3 `
bridge live parts or insulation. With another application, it may not burst since the short circuit& [: H4 _% D, v* Y7 S8 k7 ^% h( g
across a component was initiated during the zero crossing of the mains supply voltage. With
7 w6 U) T6 ]0 ^! j8 Uanother application, the fuse may burst, expelling metal pieces that bridge live parts or critical1 ^5 t9 R, A9 G1 b! a
insulation.2 e3 P. d6 ]1 n* f- a0 M- n6 t
( [7 m2 x# W" c3 ?) S- ^/ ZA bursting fuse also is not an acceptable test result in either IEC or UL component fuse( c: G, k1 @$ s$ Z/ z% r1 f/ W! U" J
standards. |
|
/1 
|关于安规|小黑屋|安规QQ群|Archiver|手机版|安规网
( 粤ICP13023453-10 )
窥视卡
雷达卡
显身卡
发表于 2011-8-21 22:58
