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附件是CTL decision sheet 416，大家讨论。. v" V* j! N* k$ m& i1 }4 ^7 y
Question:
5 d% C' x+ ^3 oEQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be' K! V, Z( E0 D) }& q
considered as LIVE, since contact with these parts could not result in excessive leakage8 m0 [# L- E$ N+ D1 j
currents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no
% c% u" J1 I1 b$ Hrequirements for safety separation between these circuits and ACCESSIBLE PARTS or2 l+ h, f# X5 z- s* i: @6 Q. |& J
APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may, G7 s! C5 l9 c4 f1 t" i
lead to currents exceeding the values given in Table IV.2 \2 J# d. p4 _- Y$ J% ?: X+ C
Decision:
i: b& L, b7 ^+ C. n. h4 l( iIf the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such
. r9 W$ U, o1 A* r( `; Finsulation should be short-circuited before determining whether a part is LIVE. This shortcircuit4 x2 L4 N3 s d, `9 L# R' `
should not be treated as a SINGLE FAULT CONDIT ION unless the insulation. ^; B+ K3 w0 w* h" G) x+ G5 t
concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION
- r5 [! Y6 I$ N3 i! C( D8 F% U& enecessary for the voltages within the isolated part.
5 z! C, B1 }) pExplanatory notes:" s' a- c& J- D: ]5 |6 J; w9 o
There are two possibilities for solving this problem. One is to change the definition of LIVE and
) L0 K* X! c. o. K8 aadopt the requirements for insulation accordingly. The second is to treat the separation of the; N* l* l# u: T0 N
isolated circuits as subject to failure.
# \* U1 G: s4 u9 {If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other: q- X! O$ ]9 \# ]1 |" N
pole becomes LIVE and the adequacy of the separation of this LIVE part under these9 O _ Y7 A) k) X' t
conditions may be assessed. If that separation is inadequate then it should be short-circuited
2 v& g9 Q; X! I1 \: F* H8 J% iin turn to assess the separation on the other pole./ j$ F' e! W& p: [ u5 V" ~! d
Since for an isolated circuit there may be two separate protective insulations (on either pole),- x6 ~0 @1 W7 Q g5 S8 d5 t! f$ Q3 _
each of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY7 h: R6 y2 G( q7 }5 m8 z- u7 g
INSULATION. Of course other combinations may be used although if the insulation of one9 y$ m" X) K1 ? t
pole is less than BASIC INSULATION then the other pole must have DOUBLE or
. Y2 v5 I# y! P+ w7 ]REINFORCED INSULATION. |
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