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| DSH 395
$ Q4 i2 r/ t$ Q, ]1 Z1 r" B% ]2 m% P' N, a
| Separation of TNV-3 and SELV circuitry
: x+ }" N( t3 ^ | 2.3.2
7 [6 B: d; N! c1 g6 G | 60950(ed.3)
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& R1 X/ F" V% [Standard(s):
( i. \8 X8 p3 N0 ?( J, \IEC 60950 (1999) 3rd Ed.4 G5 k( z; S+ b
Sub clause(s):
8 q/ ^! a. v. M; M7 [4 ]2.3.2
2 s- q2 F3 ?8 t% b9 xSheet No.
/ O$ ~" f0 b; x3 ^395& e4 |0 z9 F9 ^. _3 k% q& Z
Subject:
. M+ A9 C( U6 e+ S) bSeparation of TNV –3 and SELV0 }: e; h0 k$ X) J- s a: t+ r
circuitry4 c$ ]$ E' O: p! S; g8 g' D( D
Key words:, T- v- `, I( f i5 P" i
- Separation of TNV-3 circuit' g4 a6 R4 Q- [
and SELV circuit
/ _8 |* E! V/ _' P2 V6 iDecision taken at the 39th9 g7 x0 f1 w1 U! H; L5 q3 N: T2 _& Y
meeting 2002
5 v: n2 }# T: W' aQuestion:" w5 c2 [' l1 h4 x7 D
1. Is it permitted to demonstrate that a TNV -3 circuit is adequately separated from a SELV circuit by0 c/ b' k+ ]. ?9 X
means of single fault testing, in the situation where the spacings do not meet the requirements for basic
1 I8 e/ L$ q' ^! D- G% n% dinsulation? (The dielectric strength test is still required under Subclause 6.2.1.), u- n3 v' \; H2 N$ q& A( w5 i( `) y) y
2. If so, is it required under the compliance paragraph to short circuit the insulation between the TNVcircuit9 e6 T) T7 O% V
and the SELV circuit at all points which do not meet the criteria for basic insulation, before
" v0 W. R$ ]9 D a8 p3 V5 R$ Ccarrying out the tests?
! K" H+ C& }3 {5 m3. If short circuiting the insulation before carrying out fault tests results in the equipment passing the tests,
3 I) b8 j# u% D# ~whereas carrying out the fault tests without short circuiting the insulation would result in the equipment
8 N4 c& K* s/ S6 N& O* efailing the test, should the insulation be short circuited?
6 d) z. [$ T# ]0 o# T% z& kRationale:1 w: A) G6 r; ]7 T' R' Z! p, Q
1. Paragraph 1 of Sub-clause 2.3.2 requires that separation between a TNV-3 and a SELV circuit be such
# [. r% ^/ h v" X* T9 Jthat in the event of a single fault, the SELV circuit remains below TNV-3 limits. Paragraph 2 of Subclause
/ D; w7 ?+ p: h' N! ?2.3.2 states that basic insulation will achieve this, but other solutions are not excluded.7 r2 j7 ~- k% Y1 {! H- m, ~( a
Equipment is not required to meet either Paragraph 2 or 3. It can meet the single fault conditions stated
8 Z5 O. h( F, v% i$ v) u; Qin Paragraph one and in the compliance paragraph.
$ `! X" g, y. @& G0 L! ~% [- M" T2. According to the compliance paragraph, before carrying out the single fault tests, insulation which does+ {8 x8 N9 a @4 h/ D
not meet the requirements for basic insulation is short circuited. Presumably this does not mean that
3 R" k; w; R6 I& ~short circuits are to be applied between all tracks and components in the entire TNV-3 and SELV9 f% g$ a& | @" E! y0 t
circuitry which do not meet basic insulation, but that the insulation at the point where the TNV-3 circuit, A! C# ?4 E! z) r N( N, d3 ^
meets the SELV circuit is short-circuited.3 r* z1 i! L$ q
3. It is possible to envisage a situation where short circuiting the insulation between TNV-3 and SELV
; K* `& y3 |# Qcould cause the TNV-3 voltages to be lowered. Fault tests under this condition would not represent the( b8 o- B5 j$ H) y& r2 D1 @
worst case possible fault condition
% g8 s# K0 |. b' z+ P$ |, YDecision:
% U, K6 D+ W. a& }+ `# Y1. It is permitted to demonstrate compliance with Subclause 2.3.2 by means of single fault testing.& F! D3 T/ M* m/ V. ]7 S' e
The limits in 2.3.1.b) shall not be exceeded in normal or single fault conditions.) P' y! q0 x; e* ^2 R9 D# W; o
2. Before carrying out single fault testing of components and insulation, insulation between TNV-3 and
: z) H/ u: @, NSELV circuits not meeting the requirements of Basic insulation should be short circuited if this results in5 D+ @7 B8 f5 J
a worst case voltage measurement at accessible parts of SELV and TNV-1 circuits, and at accessible: G" r0 C0 t$ W
conductive parts during subsequent fault testing.
# T! `. j4 [: C- l* x z# X3. If the single fault test would be more severe if carried out without short circuiting the insulation, the test
1 o7 e' s' _0 q7 z2 {: H% U Tshould be done without short circuiting the insulation.% Z' x: S7 t, G f. R: O% W2 p# B
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