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附件是CTL decision sheet 416，大家讨论。
, |# O9 q1 o0 s8 pQuestion:3 z, @4 a4 k' Y6 L2 g" [7 a$ J
EQUIPMENT may contain floating circuits which under the definition 2.1.10 would not be
- F8 A4 u' t" a$ Kconsidered as LIVE, since contact with these parts could not result in excessive leakage* [% B1 F0 a; r6 x3 h+ L7 @
currents to earth or to other ACCESSIBLE PARTS. There would therefore appear to be no
6 m! R( I0 c8 B/ H. Z& t. t5 nrequirements for safety separation between these circuits and ACCESSIBLE PARTS or$ a+ G- ^# P! h1 N, ^# p0 p
APPLIED PARTS. But voltages within these circuits or in conjunction with other circuits may
7 l/ H: M& J/ M0 d+ Llead to currents exceeding the values given in Table IV.
( X( X8 O9 K6 }0 y3 m" {( mDecision:3 K6 E# x+ A, I6 X- x
If the failure of insulation of such isolated circuits is likely to lead to a SAFETY HAZARD, such$ w8 N' r* V2 i: G! c5 ?1 p
insulation should be short-circuited before determining whether a part is LIVE. This shortcircuit# o2 B+ R& g, b) v1 B
should not be treated as a SINGLE FAULT CONDIT ION unless the insulation
$ \8 a0 x5 I, @6 k7 a& n: ^concerned satisfies the requirements for BASIC or SUPPLEMENTARY INSULATION$ Y* l8 s3 V0 o/ g. c6 C7 k+ U
necessary for the voltages within the isolated part.% _" R3 e% b% c O
Explanatory notes:
m5 l. R% n0 r& q5 C+ fThere are two possibilities for solving this problem. One is to change the definition of LIVE and$ S5 \7 m' L" ?/ b! o+ s% j2 p
adopt the requirements for insulation accordingly. The second is to treat the separation of the* B& g8 ^2 U- U: g t8 \2 {/ l W
isolated circuits as subject to failure.( P+ h( T9 k/ n6 ?
If one pole of the isolated circuit is short-circuited to earth (failure of insulation) then the other F' u4 B+ V- O; O7 `) _! K' \
pole becomes LIVE and the adequacy of the separation of this LIVE part under these2 f) L5 k7 b0 }0 o+ M
conditions may be assessed. If that separation is inadequate then it should be short-circuited4 }! q% L) i2 n5 {
in turn to assess the separation on the other pole.
- x# w3 Q) j; B3 mSince for an isolated circuit there may be two separate protective insulations (on either pole),
s" }# [6 y+ G% {# ^$ Q$ T" M& Zeach of these can be BASIC INSULATION rather than BASIC and SUPPLEMENTARY
! z/ U! v# U& J3 k b$ Q3 lINSULATION. Of course other combinations may be used although if the insulation of one9 V7 P' Q' q Y9 I7 T" o/ F
pole is less than BASIC INSULATION then the other pole must have DOUBLE or5 t% v' F0 D* H; z
REINFORCED INSULATION. |
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