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附件是CTL decision sheet 416，大家讨论。
, z* e1 {; j. _+ xQuestion:- Y/ \. i2 D i- V% k) n
EQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be$ I& d' r; H) y D6 K6 Z# |
considered as LIVE, since contact with these parts could not result in excessive leakage
+ u% N5 j, ]8 u& B, ]! A2 V9 T. qcurrents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no& [: m" Y9 I6 F" Y
requirements for safety separation between these circuits and ACCESSIBLE PARTS or2 C5 M+ w* w0 `2 }% K$ g0 l$ ^
APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may- V7 m0 t* ?/ k$ t
lead to currents exceeding the values given in Table IV.6 ^& [$ d. ] t, Q' y6 K+ e
Decision:
! S2 D8 u0 F6 z; HIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such# a' o6 F. b( h" j0 ` @6 _5 l
insulation should be short-circuited before determining whether a part is LIVE. This shortcircuit5 U+ W3 f; k1 V* K" i& ^% \
should not be treated as a SINGLE FAULT CONDIT ION unless the insulation7 P1 u3 ? ~- u
concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION
Y( a) x5 c9 J, O; B4 gnecessary for the voltages within the isolated part." H M9 g$ z& \! F) R- `
Explanatory notes:9 X) r I% S# G- d4 a0 S( K
There are two possibilities for solving this problem. One is to change the definition of LIVE and% K3 x8 p4 N& V" u
adopt the requirements for insulation accordingly. The second is to treat the separation of the
" ~6 c8 C5 ^" J( ^- ]isolated circuits as subject to failure.; t9 w& @- X$ J9 J5 I1 q$ u
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other
5 B* ]% a! {* z( @- `/ Xpole becomes LIVE and the adequacy of the separation of this LIVE part under these
8 @+ y& Q0 g1 F- w: |conditions may be assessed. If that separation is inadequate then it should be short-circuited
! B& }: r- ^! g6 Y+ ^' ~5 rin turn to assess the separation on the other pole.
7 Z# @$ d5 O! M& j- e6 S- K [Since for an isolated circuit there may be two separate protective insulations (on either pole),. Y! u* @" Z! |: K4 ]) x/ A
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY
$ w( R8 y7 Q" @8 f, VINSULATION. Of course other combinations may be used although if the insulation of one
- n3 G% i1 @1 T- E, N& j/ @pole is less than BASIC INSULATION then the other pole must have DOUBLE or7 s: w, V& Z5 R/ H7 Q$ P- _
REINFORCED INSULATION. |
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