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附件是CTL decision sheet 416，大家讨论。' {4 l# Z/ e: `
Question:7 s7 C' n) q' X. z" C+ G. Y& \$ l+ z
EQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be
& ?+ ?7 N& l6 \4 [! r! sconsidered as LIVE, since contact with these parts could not result in excessive leakage( L G% d' q9 G, [
currents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no
9 S. U, w9 l& x& r4 t# urequirements for safety separation between these circuits and ACCESSIBLE PARTS or
) b- ~$ x2 ~* C' [# a! E. c* }' MAPPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may
- s0 w0 H# j0 E/ A! f$ p- r+ Alead to currents exceeding the values given in Table IV.
" T0 ^8 j5 T8 n2 FDecision:
3 T1 t- G: w2 z7 A, P) f9 QIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such
5 p$ t: k# ^* }1 k$ ~7 ainsulation should be short-circuited before determining whether a part is LIVE. This shortcircuit
$ E1 o+ h* p4 ~/ y) i6 z# c bshould not be treated as a SINGLE FAULT CONDIT ION unless the insulation
6 y. a& M5 i, jconcerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION
' I9 @" v0 [) c/ R; rnecessary for the voltages within the isolated part./ @; }4 ]* A% |" K, L6 m* w6 h
Explanatory notes:# S" u) F! a6 }+ C7 J
There are two possibilities for solving this problem. One is to change the definition of LIVE and
# {( \. P& B: y) ladopt the requirements for insulation accordingly. The second is to treat the separation of the4 A/ Q% {6 F, B( q8 g; S2 T
isolated circuits as subject to failure.$ M. `. T5 y& e0 I5 c' p& q
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other" ^ B S# W* ?% Y* w" R
pole becomes LIVE and the adequacy of the separation of this LIVE part under these$ C3 h- e7 s+ M/ p
conditions may be assessed. If that separation is inadequate then it should be short-circuited+ K C0 ~" L3 q& Q3 u$ G; ]0 o
in turn to assess the separation on the other pole.6 e- ?2 ~* e; E D
Since for an isolated circuit there may be two separate protective insulations (on either pole),( T; H; h6 q1 M2 a3 v, [
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY
2 X6 q" u4 G. q# s2 ]8 S- lINSULATION. Of course other combinations may be used although if the insulation of one3 C' v; i( a! ]% r6 |
pole is less than BASIC INSULATION then the other pole must have DOUBLE or
' X3 w4 \5 d7 W8 l( |REINFORCED INSULATION. |
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