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| DSH 395' @# [7 v, J, i* y; H/ y. Y
( L: Z: @! \1 W$ d! _$ P, L | Separation of TNV-3 and SELV circuitry- Q j; a8 L; y* ?+ Z, w! d
| 2.3.2: u6 t/ w% u: Q
| 60950(ed.3)+ H2 ~) H) M2 Y9 [2 p1 g
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/ u1 C0 U9 j6 p* V9 i' NStandard(s):
0 L# a* K6 `/ F' n1 o- l% eIEC 60950 (1999) 3rd Ed." _0 o7 v9 {' m& z) g% }8 M C
Sub clause(s):, ]9 v; u/ t7 Q5 U7 b
2.3.2
9 c7 v8 [0 U0 S$ H( F+ I# gSheet No.5 d5 F' |3 E$ n& z& k p
3955 R& e) k5 i; f- z1 U2 ^' a o
Subject:
9 ^9 S) R8 R. g& W0 x$ BSeparation of TNV –3 and SELV5 I, H5 G( F& M- @( P
circuitry! g5 Y2 {* J0 g5 [4 y: v: f6 g
Key words:2 D, Q5 Y4 \. `: u# h
- Separation of TNV-3 circuit
' X. J9 c- }. w* f1 a qand SELV circuit) w) }! U& j# l& {$ j& ~
Decision taken at the 39th
, I6 u+ j- A0 h. s" Imeeting 2002% e! ?5 L" X( r; M9 x) W( O
Question:; k4 e$ k7 {* B0 y# J$ j
1. Is it permitted to demonstrate that a TNV -3 circuit is adequately separated from a SELV circuit by
* |: I1 p& Y2 N1 {means of single fault testing, in the situation where the spacings do not meet the requirements for basic
) A7 y {4 W0 v' ~+ O# \, V4 Qinsulation? (The dielectric strength test is still required under Subclause 6.2.1.)
8 g2 Q0 i5 j+ H6 s! M! C# h2. If so, is it required under the compliance paragraph to short circuit the insulation between the TNVcircuit
$ F& A# ]0 e% ?and the SELV circuit at all points which do not meet the criteria for basic insulation, before3 @" }* t( D1 n4 Q
carrying out the tests?
+ k8 ?# R7 {& t! D* d0 h1 A3. If short circuiting the insulation before carrying out fault tests results in the equipment passing the tests,' y" h4 i) C( `" s* K# ?
whereas carrying out the fault tests without short circuiting the insulation would result in the equipment/ S$ ?# ~8 ~. J6 o) V0 D
failing the test, should the insulation be short circuited?0 p6 z: s& {: D+ p
Rationale:
5 P) F3 \1 E( a" G. U( n7 j8 s9 v1. Paragraph 1 of Sub-clause 2.3.2 requires that separation between a TNV-3 and a SELV circuit be such r$ v8 x" y( i }; T/ o4 n
that in the event of a single fault, the SELV circuit remains below TNV-3 limits. Paragraph 2 of Subclause v5 ]( A7 Q* G( O# g4 ^
2.3.2 states that basic insulation will achieve this, but other solutions are not excluded.. _& W* `& ?6 q) j! i5 G$ c
Equipment is not required to meet either Paragraph 2 or 3. It can meet the single fault conditions stated
! L, O' y" y& o! b z5 Yin Paragraph one and in the compliance paragraph., f0 e7 R1 V- z b. N
2. According to the compliance paragraph, before carrying out the single fault tests, insulation which does
3 E% _8 J" R2 Y5 {& \5 M* q& N+ jnot meet the requirements for basic insulation is short circuited. Presumably this does not mean that
Z5 u+ e$ u. nshort circuits are to be applied between all tracks and components in the entire TNV-3 and SELV
7 a4 e( G, q6 n& ?circuitry which do not meet basic insulation, but that the insulation at the point where the TNV-3 circuit
9 N+ W: U) B( k/ F3 m5 smeets the SELV circuit is short-circuited.
. d/ c( k4 j, N/ @0 y! J& Q3. It is possible to envisage a situation where short circuiting the insulation between TNV-3 and SELV
. g- Q4 l8 X* o. w) B$ b/ A+ gcould cause the TNV-3 voltages to be lowered. Fault tests under this condition would not represent the' ~, _' |3 X" \! U7 o/ b
worst case possible fault condition1 g8 `$ X; ?- G5 m- N0 p8 \3 D
Decision:2 F6 W3 [, ?7 O# J9 b% H
1. It is permitted to demonstrate compliance with Subclause 2.3.2 by means of single fault testing.
" N# \# K7 a1 j/ _ h( q8 kThe limits in 2.3.1.b) shall not be exceeded in normal or single fault conditions." N) ^: X$ [( [5 s2 t
2. Before carrying out single fault testing of components and insulation, insulation between TNV-3 and
1 m- R$ P$ Z; m% v" z' p6 sSELV circuits not meeting the requirements of Basic insulation should be short circuited if this results in3 D- T1 p$ _% R
a worst case voltage measurement at accessible parts of SELV and TNV-1 circuits, and at accessible, C3 U9 i- T& @6 \2 t4 s) @
conductive parts during subsequent fault testing.5 A: g2 o4 Q: y& M$ ]$ m
3. If the single fault test would be more severe if carried out without short circuiting the insulation, the test
8 x) v( P' C0 fshould be done without short circuiting the insulation.& v+ [" ~ p# w+ H
g- W3 U/ `4 E! x. B
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