Separation of TNV-3 and SELV circuitry. c! d( g. B4 H) |
2.3.2 " P/ j* C7 ^* d/ G9 v* k: v
60950(ed.3)$ K1 P% E# ]4 p. R( l) |/ K
" P l( N2 `" B" U: zStandard(s): / P/ I5 y: J( v6 AIEC 60950 (1999) 3rd Ed. & w- W) P" w) W6 Y4 Y7 T) k! pSub clause(s):' ~7 V9 @9 F) [5 O
2.3.2 : l: L- z) W3 n7 M \2 u M8 U/ O- C7 wSheet No. 2 x3 V$ f+ {6 m. x) @2 g& Z1 Z( I) I3953 W2 Z3 D) y; H( o$ @; B
Subject: $ f1 d8 A* x2 \* E% E. S/ uSeparation of TNV –3 and SELV 0 y$ M/ g. Q* @" ?& {$ D2 Pcircuitry ! I# d* R1 f! @& R5 ]. AKey words:5 Y, l v! q. K$ V6 j
- Separation of TNV-3 circuit3 p. P6 _) t; s
and SELV circuit + } U2 X5 l8 K) Y3 rDecision taken at the 39th ) L( @8 u0 N0 w" Y: jmeeting 20026 d. e1 B$ M/ ^# [: V
Question: 6 F& ~, t4 Y" @2 P3 q" m1. Is it permitted to demonstrate that a TNV -3 circuit is adequately separated from a SELV circuit by9 ~1 D# |. x6 O1 ?8 |0 m9 X) X
means of single fault testing, in the situation where the spacings do not meet the requirements for basic$ O: Q1 m. Q3 ]4 A6 }+ u6 D* W
insulation? (The dielectric strength test is still required under Subclause 6.2.1.) 5 V- W" I% a. |) a% b5 i( [) C+ t2. If so, is it required under the compliance paragraph to short circuit the insulation between the TNVcircuit& g. H8 _1 j! E- s4 ^* x( O
and the SELV circuit at all points which do not meet the criteria for basic insulation, before$ Z/ O s `7 Q2 t4 R
carrying out the tests?4 {5 [+ p" q' S6 _0 {) |/ n- l# S4 Q
3. If short circuiting the insulation before carrying out fault tests results in the equipment passing the tests,' M3 l9 @) Z/ d6 p- G5 e x# `
whereas carrying out the fault tests without short circuiting the insulation would result in the equipment " c) M0 U7 \ u- p) l: |4 vfailing the test, should the insulation be short circuited?2 H9 w; R! y8 d, X
Rationale: , `. b9 Q1 y8 z1. Paragraph 1 of Sub-clause 2.3.2 requires that separation between a TNV-3 and a SELV circuit be such6 E% Z' G7 U1 t- ]* b {- i
that in the event of a single fault, the SELV circuit remains below TNV-3 limits. Paragraph 2 of Subclause, Y# n1 A1 E/ B# w; M# W
2.3.2 states that basic insulation will achieve this, but other solutions are not excluded. $ Z( }! s& b4 M P# [% J, ~& lEquipment is not required to meet either Paragraph 2 or 3. It can meet the single fault conditions stated ) v) D2 J2 v, }4 U: y! W; O+ e: Sin Paragraph one and in the compliance paragraph. + H8 B+ S5 {' `$ P2. According to the compliance paragraph, before carrying out the single fault tests, insulation which does, {* J& ~& e* q7 M5 {9 g
not meet the requirements for basic insulation is short circuited. Presumably this does not mean that7 C" X- V9 |* a, a% |7 I1 |
short circuits are to be applied between all tracks and components in the entire TNV-3 and SELV( z( m, W- q$ S) b* Z/ W% X
circuitry which do not meet basic insulation, but that the insulation at the point where the TNV-3 circuit 8 v2 W8 c+ N; J5 e! M( {( gmeets the SELV circuit is short-circuited. 1 m4 D* S: `/ r' i# d3. It is possible to envisage a situation where short circuiting the insulation between TNV-3 and SELV : _8 ?( [8 ?, f3 a& [- Q* [- Hcould cause the TNV-3 voltages to be lowered. Fault tests under this condition would not represent the 7 T1 [1 }, p9 Y+ [1 y4 \0 Q( ~, [worst case possible fault condition : Z8 _7 y4 ~# A: q5 H. eDecision:# O$ ^- i9 ]. b' Z D, @4 I
1. It is permitted to demonstrate compliance with Subclause 2.3.2 by means of single fault testing.3 i. a7 H& b7 I D9 N: |- ]
The limits in 2.3.1.b) shall not be exceeded in normal or single fault conditions. 8 g8 \' Q+ c8 s8 y- F2. Before carrying out single fault testing of components and insulation, insulation between TNV-3 and- v1 V% M4 |' E
SELV circuits not meeting the requirements of Basic insulation should be short circuited if this results in % [& U( l1 J9 R! d, w% Ea worst case voltage measurement at accessible parts of SELV and TNV-1 circuits, and at accessible : G3 R. y X$ O0 Dconductive parts during subsequent fault testing.( V9 O, O) `! b
3. If the single fault test would be more severe if carried out without short circuiting the insulation, the test & X' J+ s( G' ]" Dshould be done without short circuiting the insulation.; T6 {3 a% L r0 m: z
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