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附件是CTL decision sheet 416，大家讨论。/ M w2 j4 P$ v$ m8 Q0 ?+ N* ^
Question:
1 f! m4 p6 @. |4 x4 MEQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be& w% q5 E4 q! G5 @7 }+ E# r
considered as LIVE, since contact with these parts could not result in excessive leakage a+ U& }% x. u. {; ]% p B
currents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no
7 T% k3 q% i' Krequirements for safety separation between these circuits and ACCESSIBLE PARTS or- g% N7 A7 B8 J* F# Y2 P; Z
APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may
5 ~: p% c1 h' C. n1 ?( jlead to currents exceeding the values given in Table IV.% d/ |8 H* i+ Q$ a, o% x- W
Decision:. {& c8 H5 h. V- `7 A, w
If the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such
8 V* U) A7 m% R2 l1 o% yinsulation should be short-circuited before determining whether a part is LIVE. This shortcircuit# C0 o6 s! T( _1 U0 a( W# K: P3 }
should not be treated as a SINGLE FAULT CONDIT ION unless the insulation
9 s, [+ m _% T! I) K/ `concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION
$ i7 }; k7 O/ S% A4 |) P4 W/ onecessary for the voltages within the isolated part.3 j" e2 G! H9 Z% ~ ^! K
Explanatory notes:
& g5 P4 V5 W. d1 x. yThere are two possibilities for solving this problem. One is to change the definition of LIVE and6 Q# _ i! k; A3 i0 T+ Z; g" a
adopt the requirements for insulation accordingly. The second is to treat the separation of the$ O, L+ D, e, W4 H: {( f2 e
isolated circuits as subject to failure. _$ ?% L0 }+ V3 G, j7 k# U' e
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other
" @( _# g8 k/ \7 w" a. upole becomes LIVE and the adequacy of the separation of this LIVE part under these
7 p @ |+ {3 Kconditions may be assessed. If that separation is inadequate then it should be short-circuited
* _# j9 `! K W7 s! A& din turn to assess the separation on the other pole.6 t3 j$ p8 ?0 ^3 s6 W7 h4 U: o
Since for an isolated circuit there may be two separate protective insulations (on either pole),1 z* F! t" X3 j9 l/ J
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY
, O2 d. `6 C( SINSULATION. Of course other combinations may be used although if the insulation of one% L$ @, }5 I, k& x
pole is less than BASIC INSULATION then the other pole must have DOUBLE or
, g( R( W( u: h/ H) wREINFORCED INSULATION. |
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