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附件是CTL decision sheet 416，大家讨论。
% N, T- C; w6 m! W3 w5 ^Question:- k# w8 H9 A# R
EQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be4 o$ b- p" h8 `1 ?2 g
considered as LIVE, since contact with these parts could not result in excessive leakage. l3 t- @, }( |: c
currents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no. B& w% u2 _; X6 {1 [
requirements for safety separation between these circuits and ACCESSIBLE PARTS or
* L& X% `5 Y+ T& \/ ~: SAPPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may
0 J a; q; v5 O9 Flead to currents exceeding the values given in Table IV.9 ]8 A0 c0 M# D" z7 @4 e
Decision:
! l; X6 f. ]. Y) ?- ?" h2 cIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such! k2 G$ w' h, B6 ~ T
insulation should be short-circuited before determining whether a part is LIVE. This shortcircuit
, S; P' o) K, ` j' Dshould not be treated as a SINGLE FAULT CONDIT ION unless the insulation6 z9 T9 H+ p0 D4 O
concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION5 ~4 u* Z) @& ~8 `; M: R
necessary for the voltages within the isolated part.
4 u( n7 t; C% |/ w! ^% S( |Explanatory notes:
( {7 I5 l4 t+ ~; dThere are two possibilities for solving this problem. One is to change the definition of LIVE and& U6 i( h! ]! b, f3 b0 }+ p
adopt the requirements for insulation accordingly. The second is to treat the separation of the3 Z8 c) \+ c8 b% X
isolated circuits as subject to failure.1 f+ O' s( ~1 y' V9 y- o8 N
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other
) d+ y* f* W/ q! F% ]pole becomes LIVE and the adequacy of the separation of this LIVE part under these
* w2 h! i7 b+ Cconditions may be assessed. If that separation is inadequate then it should be short-circuited
6 _/ L" ^0 }9 p' Win turn to assess the separation on the other pole.
" o" {2 E& b# m' l. V, I# KSince for an isolated circuit there may be two separate protective insulations (on either pole),( ]5 {( y; i7 u. R, |& {
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY
* ]/ x% _, J( Y7 Y8 VINSULATION. Of course other combinations may be used although if the insulation of one+ j# L8 L$ V6 X, X+ h% v6 ?
pole is less than BASIC INSULATION then the other pole must have DOUBLE or; [! F) z3 ]6 T T. G; A
REINFORCED INSULATION. |
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