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附件是CTL decision sheet 416，大家讨论。! R' T) h% h! A' E7 B
Question:
+ c3 B4 N4 u6 sEQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be* u `7 M8 K& T }, L& b, D
considered as LIVE, since contact with these parts could not result in excessive leakage
; s5 m1 c; ? K, p! n. F Gcurrents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no% v3 B) g8 _$ B. T6 n
requirements for safety separation between these circuits and ACCESSIBLE PARTS or% r+ z( p( ?5 ]+ L3 w
APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may6 g% o& a& y( G5 j3 v4 s+ J
lead to currents exceeding the values given in Table IV.
9 I0 ~$ B& `% J7 B! dDecision:
t) |8 i: N) \1 e6 I* ]) C( ~% r' ZIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such
! K. x! J2 h2 @$ Dinsulation should be short-circuited before determining whether a part is LIVE. This shortcircuit) y4 h3 t% v& a& \7 L+ v
should not be treated as a SINGLE FAULT CONDIT ION unless the insulation! K8 y U( U6 x2 d/ d3 Z n
concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION' W5 E" k7 s( ~2 B. F7 k0 x. l. Q& B
necessary for the voltages within the isolated part.
! `1 O- u s! ~8 Q6 P' @Explanatory notes:
7 W8 j" ]# A4 n$ ?- N5 t. _There are two possibilities for solving this problem. One is to change the definition of LIVE and
8 f8 e1 y0 I+ n- I) k. Oadopt the requirements for insulation accordingly. The second is to treat the separation of the
6 j) [3 Q t; |+ `1 R5 P2 {6 i5 eisolated circuits as subject to failure., X8 u+ ]: V: u2 }! \" P
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other4 u8 H# Z# |" v' L1 ~
pole becomes LIVE and the adequacy of the separation of this LIVE part under these: \+ E: p2 V* @- a$ `1 |% H6 P
conditions may be assessed. If that separation is inadequate then it should be short-circuited
0 f2 ]) l7 s( N; y4 }$ Qin turn to assess the separation on the other pole.
9 v3 N, p& T. f! w* ]# m8 X1 RSince for an isolated circuit there may be two separate protective insulations (on either pole),! y& C% f8 w w6 _6 ^, p
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY' S) |5 a, g) g z3 n( ~" {8 G- P3 @
INSULATION. Of course other combinations may be used although if the insulation of one
" h# l2 m# `* b0 w5 kpole is less than BASIC INSULATION then the other pole must have DOUBLE or, d) n3 S j" k% _0 k
REINFORCED INSULATION. |
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