Separation of TNV-3 and SELV circuitry- V1 d! y& J; I$ Q+ t4 s, @4 ~0 j
2.3.2 - X" x/ K7 ?4 i
60950(ed.3)0 v z) T" y$ {+ J) Q7 e/ F/ `; {9 W y
# }% t' I& \9 u+ ]: e2 ZStandard(s):3 X/ e. y! O% J8 A2 W5 ^& K6 _, T5 `
IEC 60950 (1999) 3rd Ed. 9 F' e( n, A v3 Q# E/ d! L( rSub clause(s): / u5 f# M; s6 m X: |; h2.3.2 3 S, l b2 v' m9 TSheet No.' @- s* P: K+ j, E
395 ( C% s" a( i4 {! ~7 g' C: _2 {Subject:% w) }+ I f: X4 |$ \
Separation of TNV –3 and SELV, X" r) k L/ A& ]! ~; Q
circuitry/ [8 {3 w0 e# w8 D
Key words:* b$ Y! i0 P! Y/ _% ?
- Separation of TNV-3 circuit ! T3 B; B# j, M, \* z, T4 uand SELV circuit " u+ j1 ~$ M- Y6 `- b% TDecision taken at the 39th : z/ w7 S. [0 g5 Gmeeting 2002 / L* @# J5 i b- WQuestion: / y! ]: i, U; D9 [+ V. A/ z1. Is it permitted to demonstrate that a TNV -3 circuit is adequately separated from a SELV circuit by$ K( `5 M; t8 X9 a( d. ~" i
means of single fault testing, in the situation where the spacings do not meet the requirements for basic9 o5 P9 X! u! H; ?) H
insulation? (The dielectric strength test is still required under Subclause 6.2.1.) b( d9 B! [1 i$ M; V$ C r2. If so, is it required under the compliance paragraph to short circuit the insulation between the TNVcircuit0 D9 p" q8 c7 I$ y3 p
and the SELV circuit at all points which do not meet the criteria for basic insulation, before . V% }; s, B$ e% f9 Rcarrying out the tests?5 P8 P# q6 |& ?3 W9 F& ?4 h! R
3. If short circuiting the insulation before carrying out fault tests results in the equipment passing the tests, , i$ z* n2 Y2 s4 e- M, dwhereas carrying out the fault tests without short circuiting the insulation would result in the equipment+ \( N% a P* G3 e9 m8 I4 o8 @1 H
failing the test, should the insulation be short circuited?8 f% C0 i; r% ^
Rationale:; K5 B( ~/ P. u) {% e7 q. p X) t1 K
1. Paragraph 1 of Sub-clause 2.3.2 requires that separation between a TNV-3 and a SELV circuit be such 4 S7 B7 Z0 d* u5 \that in the event of a single fault, the SELV circuit remains below TNV-3 limits. Paragraph 2 of Subclause0 w; l4 k- Q8 B" ?4 ]7 ?
2.3.2 states that basic insulation will achieve this, but other solutions are not excluded.- r7 _& }# Q( Z8 T6 O( S0 p
Equipment is not required to meet either Paragraph 2 or 3. It can meet the single fault conditions stated : L8 I" `, W; y. ` E& ^8 pin Paragraph one and in the compliance paragraph. ! S; Q( \$ p! p) q; n) ~2. According to the compliance paragraph, before carrying out the single fault tests, insulation which does( Z. m# q' ]' d4 M
not meet the requirements for basic insulation is short circuited. Presumably this does not mean that 3 U5 p1 M1 p6 X* z/ ~2 ^: tshort circuits are to be applied between all tracks and components in the entire TNV-3 and SELV ) G1 ^- a! G/ U$ V& `7 Mcircuitry which do not meet basic insulation, but that the insulation at the point where the TNV-3 circuit : j- ^4 k$ n Bmeets the SELV circuit is short-circuited. 2 \+ C7 D' K3 i# v- }! y3. It is possible to envisage a situation where short circuiting the insulation between TNV-3 and SELV2 o1 J2 Y+ N$ S2 s
could cause the TNV-3 voltages to be lowered. Fault tests under this condition would not represent the , I% t9 g8 h! Wworst case possible fault condition6 m4 u) ]* \! j t$ A5 X" s) l: u
Decision:, a2 l3 F! {4 a' |
1. It is permitted to demonstrate compliance with Subclause 2.3.2 by means of single fault testing.+ W2 r {* O5 y7 c `6 z0 l" }
The limits in 2.3.1.b) shall not be exceeded in normal or single fault conditions.3 u( n1 `6 y3 ^6 q
2. Before carrying out single fault testing of components and insulation, insulation between TNV-3 and % W) K1 Y/ L- j1 K7 G/ W6 U( xSELV circuits not meeting the requirements of Basic insulation should be short circuited if this results in 1 E7 O; U2 g. H4 G8 A+ ]a worst case voltage measurement at accessible parts of SELV and TNV-1 circuits, and at accessible4 V. } f' {- L/ `4 H
conductive parts during subsequent fault testing., W) Y' g6 H4 B3 C ^% e; y
3. If the single fault test would be more severe if carried out without short circuiting the insulation, the test, \' X5 X6 v9 X4 q
should be done without short circuiting the insulation.* ~' ^1 C2 W( J& _8 ?; c3 K
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[attach]77166[/attach] $ ~+ u# Q) A8 a" \! S* `- S6 x
DSH 395