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附件是CTL decision sheet 416，大家讨论。
$ Y* |& M# y' E6 H/ J, E4 wQuestion:
: N) {, A9 T8 }$ A+ v( W2 LEQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be7 l4 K0 B; Q) k6 K; F% g
considered as LIVE, since contact with these parts could not result in excessive leakage
, m) M- J8 b" V5 @" Q' W+ @currents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no
1 c p( Z7 D( A' c' |2 Irequirements for safety separation between these circuits and ACCESSIBLE PARTS or
, H g0 t: s' U+ p- m R* \3 |APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may
3 D& |& f+ O) [# M* U+ ]: Clead to currents exceeding the values given in Table IV.
7 `: L1 D8 N3 h# _/ i, \& |Decision:0 ?2 P* u# d4 ^5 s9 a6 x* h
If the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such1 @+ _' m) K* E2 m
insulation should be short-circuited before determining whether a part is LIVE. This shortcircuit( B5 V# E4 g0 C' ^) `- r
should not be treated as a SINGLE FAULT CONDIT ION unless the insulation' p8 M x# R5 U
concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION
+ f6 M# a+ ?/ T9 ?necessary for the voltages within the isolated part.
# v* y7 I) d5 l( u# q1 q; qExplanatory notes:) n* _% v+ @5 J, {" v9 @4 C3 D; D3 M
There are two possibilities for solving this problem. One is to change the definition of LIVE and
/ y7 X3 K) s- m- ]% q8 Qadopt the requirements for insulation accordingly. The second is to treat the separation of the
9 N+ `$ D$ o; f2 I# wisolated circuits as subject to failure.* C8 y7 S, J+ A: i6 h( L
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other7 o+ Z' O1 }' n
pole becomes LIVE and the adequacy of the separation of this LIVE part under these- t0 T1 ?" r8 r5 T* C
conditions may be assessed. If that separation is inadequate then it should be short-circuited
( e& ~! s5 l( K4 ~! d4 U" Vin turn to assess the separation on the other pole.* m/ Y' ?+ t' X* q' {
Since for an isolated circuit there may be two separate protective insulations (on either pole),0 n, x, y9 o0 G! ~- M
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY: g4 a2 r8 a- ]5 e: u% P9 L7 T- {8 F
INSULATION. Of course other combinations may be used although if the insulation of one7 H4 j7 l J) V( a' }% S; T
pole is less than BASIC INSULATION then the other pole must have DOUBLE or. W" K6 G0 Z: l$ y% P
REINFORCED INSULATION. |
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