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附件是CTL decision sheet 416，大家讨论。
) P- u3 }+ n9 x( g J3 v. U- `# zQuestion:
9 I' p+ K7 b' r& L6 U, EEQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be
5 t$ t4 }# m1 g7 n) Cconsidered as LIVE, since contact with these parts could not result in excessive leakage
) [" Q$ s) h9 \+ V# icurrents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no
) W/ _" Y2 I# {requirements for safety separation between these circuits and ACCESSIBLE PARTS or
: m" Z1 i7 |2 C% z( b$ X4 D1 F7 ~APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may
, V$ y, } y+ V% ~7 l' {5 p& U5 M4 Glead to currents exceeding the values given in Table IV.1 z& l) \1 E2 O: Q+ S5 [0 `
Decision:
$ N, q6 y' F* ~7 Y7 aIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such. U+ f8 |! t7 S8 f* ~- V1 Q! k
insulation should be short-circuited before determining whether a part is LIVE. This shortcircuit
2 Y0 p: |. G Ashould not be treated as a SINGLE FAULT CONDIT ION unless the insulation+ M# Q! R/ H( d( U% ^7 w, |8 u# Y
concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION! I" v1 l# q3 `2 @; w
necessary for the voltages within the isolated part.
" l/ Y) z, ^. ]$ RExplanatory notes:9 U7 y; u @! |' u
There are two possibilities for solving this problem. One is to change the definition of LIVE and: V7 } Z; ?, ?: D- l
adopt the requirements for insulation accordingly. The second is to treat the separation of the
& C5 v" w7 a3 z e. Disolated circuits as subject to failure.! m2 A0 J7 ~% H
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other
# j2 U. Y( V9 V E( g ]pole becomes LIVE and the adequacy of the separation of this LIVE part under these& c7 C1 y5 D8 u. ^2 Z1 ?# \
conditions may be assessed. If that separation is inadequate then it should be short-circuited. [' V6 J) W3 S; m/ ^) ?; x- x
in turn to assess the separation on the other pole.+ Q2 U( [2 e/ m4 {& J. e" y
Since for an isolated circuit there may be two separate protective insulations (on either pole),) A- g/ W8 x4 @; F' A/ l
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY4 T5 x' O& \ w, y8 V
INSULATION. Of course other combinations may be used although if the insulation of one
/ S* Z; h i9 Y* gpole is less than BASIC INSULATION then the other pole must have DOUBLE or
" X$ F* u- V! o' K6 F$ d7 qREINFORCED INSULATION. |
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