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附件是CTL decision sheet 416，大家讨论。* W+ C/ b2 ^! ?/ ^4 ~
Question:
) ]# ^: G n' k6 y- y/ a2 wEQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be# N- o) y% I3 r$ ?' k, U$ V! C
considered as LIVE, since contact with these parts could not result in excessive leakage
; J2 m: ^2 l; p* N1 E# U+ Vcurrents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no% H# V" m+ F4 Y/ Z
requirements for safety separation between these circuits and ACCESSIBLE PARTS or
8 D- a1 b4 ]" f/ U; jAPPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may" [ @2 D+ ~: [6 D; u. T
lead to currents exceeding the values given in Table IV.
5 M4 g, r! U+ K' Y4 HDecision:
5 A/ G; M6 W" G6 ?+ L/ x- {2 u4 h$ z) PIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such, q9 e% `5 P. F/ {* h# g3 R
insulation should be short-circuited before determining whether a part is LIVE. This shortcircuit L& S( \1 N+ g! c7 ~2 W
should not be treated as a SINGLE FAULT CONDIT ION unless the insulation
4 e8 G# j0 w. @7 f/ hconcerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION1 e, n3 z4 @. K$ s) H K
necessary for the voltages within the isolated part.
5 `( q8 K1 q% D" ^7 A: v. GExplanatory notes:
, {; l* p/ Y- q" o1 j" ^) _, ~There are two possibilities for solving this problem. One is to change the definition of LIVE and
+ \9 X$ r5 }' s V; a+ @; tadopt the requirements for insulation accordingly. The second is to treat the separation of the
6 v9 B7 j/ B4 z5 r7 {2 e, Wisolated circuits as subject to failure.
8 k) j% W& a3 IIf one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other) y ^, h7 K d4 K5 ?4 k2 n
pole becomes LIVE and the adequacy of the separation of this LIVE part under these3 F7 p& v0 a* Z. J# H
conditions may be assessed. If that separation is inadequate then it should be short-circuited
o3 r1 x9 k! O6 }' jin turn to assess the separation on the other pole./ A- I x# I, h% Y+ ?! c7 i7 i+ {9 A
Since for an isolated circuit there may be two separate protective insulations (on either pole),
8 \& O, B1 K! L% Qeach of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY7 [) r: t& v' m
INSULATION. Of course other combinations may be used although if the insulation of one
. y1 F+ Q" W; O' ^9 f C; xpole is less than BASIC INSULATION then the other pole must have DOUBLE or
" G) G+ a, U9 Z; {7 p) L: TREINFORCED INSULATION. |
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