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附件是CTL decision sheet 416，大家讨论。
* F/ w! o, _7 i& Q: c* T. HQuestion:
( q* x5 [+ e+ i. u- N+ XEQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be
8 u) @1 m' ^! Q! b: h' M0 D2 ^considered as LIVE, since contact with these parts could not result in excessive leakage$ @# ?6 [$ s9 B0 V( N' Q; K
currents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no# W6 H w+ ?5 ]$ l
requirements for safety separation between these circuits and ACCESSIBLE PARTS or
$ Q2 }' R# C7 U& iAPPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may
8 Q$ `! }- o$ T5 }) p! D$ Dlead to currents exceeding the values given in Table IV.: O, c5 K4 b; U1 Z# R, E
Decision:
, j, r# b$ J* o, KIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such6 V9 ~ s4 T1 O8 H6 y' V6 |7 }
insulation should be short-circuited before determining whether a part is LIVE. This shortcircuit
- {% C, u- D- w& j2 Z3 U2 O" l8 Tshould not be treated as a SINGLE FAULT CONDIT ION unless the insulation/ k4 X/ v7 L5 s: W- u- F8 |$ A
concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION" l8 S( k0 y& o# C
necessary for the voltages within the isolated part.) C4 T" }/ F" l$ m7 y! @0 L
Explanatory notes:! K7 n! @' N6 D- o! i
There are two possibilities for solving this problem. One is to change the definition of LIVE and
+ [! z. j! n' L. U8 u* V9 Kadopt the requirements for insulation accordingly. The second is to treat the separation of the6 y% ]! d/ ? c# E) k
isolated circuits as subject to failure., A+ A$ n* [0 l) I* _( ^9 Y3 ?
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other
7 G5 b" O# P* G1 l9 q6 n9 apole becomes LIVE and the adequacy of the separation of this LIVE part under these I5 U4 R: d2 d- |4 i4 {( `5 Z
conditions may be assessed. If that separation is inadequate then it should be short-circuited" T, l+ g0 S( v9 H
in turn to assess the separation on the other pole.
& Y# ^' U( j" t3 F P3 h& NSince for an isolated circuit there may be two separate protective insulations (on either pole),
$ z0 s& j l, a6 B! q. [1 d. {each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY
1 i/ e; g% Y( x7 Q P0 t* @INSULATION. Of course other combinations may be used although if the insulation of one
[9 u6 H( ~7 ?- I4 |pole is less than BASIC INSULATION then the other pole must have DOUBLE or
- F( c1 ~4 N J1 ]REINFORCED INSULATION. |
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