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附件是CTL decision sheet 416，大家讨论。
# A& X/ d M% q8 `7 YQuestion:$ p) l+ e5 l0 C. b- p, B
EQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be- A7 z6 ~% K# ~ q; F" v
considered as LIVE, since contact with these parts could not result in excessive leakage
* ]( _: v1 B* O% rcurrents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no; Y9 y' {0 K; K) R, M+ [$ ^, g. o9 k
requirements for safety separation between these circuits and ACCESSIBLE PARTS or3 q: l- }, e; w8 A" \* x8 C% v
APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may' z% u! m! Y8 e0 i
lead to currents exceeding the values given in Table IV.- C C& O3 G0 B; S% b( e1 P1 S6 E
Decision:
7 Z1 ^* w4 ` f9 PIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such0 l& a# k7 j! H
insulation should be short-circuited before determining whether a part is LIVE. This shortcircuit
G4 o& K' S( }. I2 e. r* M2 xshould not be treated as a SINGLE FAULT CONDIT ION unless the insulation
& Y4 N. H9 u/ s L, ]concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION0 o) o* _: G7 t
necessary for the voltages within the isolated part.
; Q% k' g; x$ p* ?9 UExplanatory notes:. T* h, Q4 ~" W) w. N5 O" @" [
There are two possibilities for solving this problem. One is to change the definition of LIVE and: u* c) {" h4 A/ ]8 x* E
adopt the requirements for insulation accordingly. The second is to treat the separation of the
6 h: ~7 ~- e6 qisolated circuits as subject to failure.
3 S; _" o1 s f' P) d1 H8 k. L. vIf one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other
6 [, n: J- U5 L% I7 X! W& cpole becomes LIVE and the adequacy of the separation of this LIVE part under these1 z) m- Q' o. e0 F4 }' ~
conditions may be assessed. If that separation is inadequate then it should be short-circuited5 |- F$ h: D. e, Q6 O4 s+ K! U
in turn to assess the separation on the other pole.
' F2 L8 M2 ]$ PSince for an isolated circuit there may be two separate protective insulations (on either pole),; C4 Z" [! A% R' d/ e5 t9 I, ]1 U W
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY3 F& ?6 p! b8 T/ C1 L9 V/ U
INSULATION. Of course other combinations may be used although if the insulation of one
\7 t: A. \/ I) a) vpole is less than BASIC INSULATION then the other pole must have DOUBLE or
0 z2 P6 n# W$ P9 `: ?REINFORCED INSULATION. |
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