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附件是CTL decision sheet 416,大家讨论。
1 L) Q% y1 Q* @; u# S" _* yQuestion:4 R; G; E. M7 I; J! ]
EQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be) A8 |( k) K5 r/ r
considered as LIVE, since contact with these parts could not result in excessive leakage7 u: z2 c3 p$ F$ Q" Y; w
currents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no& l" {1 u2 F8 I) ^2 `
requirements for safety separation between these circuits and ACCESSIBLE PARTS or
2 Q0 s( U. O O$ {APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may% O7 C/ v9 Z/ G* ~! T/ \+ c! k6 `) L
lead to currents exceeding the values given in Table IV.
/ C: u s c; I6 |" eDecision:$ R# F7 V2 g0 [; |8 T
If the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such
5 H8 h! z' o5 c; V1 }3 b+ H; m0 T: dinsulation should be short-circuited before determining whether a part is LIVE. This shortcircuit: s4 q* @% {. {5 t d
should not be treated as a SINGLE FAULT CONDIT ION unless the insulation
4 B$ \1 Z% I# C, ~concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION0 W% D0 A, k4 v1 K
necessary for the voltages within the isolated part.6 s; H1 [" c8 Z" a- h5 a- x8 j6 B- k
Explanatory notes:$ s4 k! {: U2 T% _4 H6 X4 L, y
There are two possibilities for solving this problem. One is to change the definition of LIVE and+ ^3 G4 ?; U9 U" K
adopt the requirements for insulation accordingly. The second is to treat the separation of the
1 n5 {1 A; P* r( ]: yisolated circuits as subject to failure.+ J, l+ B d; k% j
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other1 M+ W! V0 I& f j# a6 S' c1 V
pole becomes LIVE and the adequacy of the separation of this LIVE part under these% y5 d( j7 ~, `1 r" i
conditions may be assessed. If that separation is inadequate then it should be short-circuited# ^4 D' ?0 Z: Z
in turn to assess the separation on the other pole./ Y3 e: U# q. {+ h; y9 U
Since for an isolated circuit there may be two separate protective insulations (on either pole),1 n' p2 n$ u4 B% B/ E
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY" S2 U0 I1 ], [8 C1 M' [& b& F
INSULATION. Of course other combinations may be used although if the insulation of one) ~) g% ?5 t& q& N0 Z6 r5 T$ t
pole is less than BASIC INSULATION then the other pole must have DOUBLE or, ~4 `% V1 ^% I R* Q1 \
REINFORCED INSULATION. |
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