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| DSH 395
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# y/ W3 z5 r4 C. m: h2 b/ S7 w9 N | Separation of TNV-3 and SELV circuitry5 M' M) y: ]: z; D
| 2.3.2
, a4 T" b& ] o" K! a | 60950(ed.3)
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% j* ~ l. R! |3 AStandard(s):
- S- T7 k0 ?/ |0 k2 E; `2 bIEC 60950 (1999) 3rd Ed.
' }( H8 M, M1 b# B2 p$ z @* FSub clause(s):
) D% W& m' G3 L2.3.2; Y- H7 x( I/ a. T4 g- y
Sheet No.
5 t6 b6 g4 _% U; N# @9 K395; t) y# H$ R. U+ b
Subject:) t3 |' \8 {/ K
Separation of TNV –3 and SELV
8 }9 q5 ~! [3 C" m- i* zcircuitry
" [) ]% G2 F- A) O8 @Key words:
; _7 ^9 w1 c# |: f+ V# `; H- Separation of TNV-3 circuit5 {4 |3 t) u, `9 p4 D
and SELV circuit) g# I2 @7 g* p& K" n" X
Decision taken at the 39th
# k5 d: }5 f' o- H+ L( w' M& Qmeeting 2002
' I. s9 W: g9 C; r# Z, fQuestion:3 X1 ~! ]7 ~2 V" N
1. Is it permitted to demonstrate that a TNV -3 circuit is adequately separated from a SELV circuit by* B2 k! B& V( \ f- F) g
means of single fault testing, in the situation where the spacings do not meet the requirements for basic
- G0 E1 {, j Y9 yinsulation? (The dielectric strength test is still required under Subclause 6.2.1.)
5 O& Z c) W( J- V4 `. l6 o2. If so, is it required under the compliance paragraph to short circuit the insulation between the TNVcircuit4 X: D# a B- ? E' D' Y
and the SELV circuit at all points which do not meet the criteria for basic insulation, before( O; x( v4 ~& C; h
carrying out the tests?
/ T& v1 [, p- u d% i [7 T3. If short circuiting the insulation before carrying out fault tests results in the equipment passing the tests,
! ]( o: j$ y% Z- n& e# }7 Z% @whereas carrying out the fault tests without short circuiting the insulation would result in the equipment% Q7 N. }5 V7 T6 r* G0 C0 i
failing the test, should the insulation be short circuited?8 T4 j9 w1 x$ }8 F
Rationale:
' R) o# f% D; j! u# ?/ D6 p1. Paragraph 1 of Sub-clause 2.3.2 requires that separation between a TNV-3 and a SELV circuit be such
# ?' R5 `8 i& s! kthat in the event of a single fault, the SELV circuit remains below TNV-3 limits. Paragraph 2 of Subclause% k7 X1 l$ K8 }2 W$ q
2.3.2 states that basic insulation will achieve this, but other solutions are not excluded.
. z- N& I% `. I v1 CEquipment is not required to meet either Paragraph 2 or 3. It can meet the single fault conditions stated& a5 e y, a. j9 f) j* g, z
in Paragraph one and in the compliance paragraph.
4 t0 k4 L8 H+ o7 l2 n' m8 F% Z- H% l0 g2. According to the compliance paragraph, before carrying out the single fault tests, insulation which does/ `0 P: S7 C1 Y6 U, q7 L
not meet the requirements for basic insulation is short circuited. Presumably this does not mean that& ~* ?7 Z( q t$ M& g: \& }! ^
short circuits are to be applied between all tracks and components in the entire TNV-3 and SELV
+ |) [) ]1 l1 n( k8 P4 ycircuitry which do not meet basic insulation, but that the insulation at the point where the TNV-3 circuit
/ ^+ a& t+ ^9 Ameets the SELV circuit is short-circuited.
# J! {& {5 v9 G3 d, |3. It is possible to envisage a situation where short circuiting the insulation between TNV-3 and SELV
6 F# Q1 b4 S- _2 e# T+ qcould cause the TNV-3 voltages to be lowered. Fault tests under this condition would not represent the
$ ]2 O& u/ B, D& Mworst case possible fault condition$ z' @$ Z5 @" v& Q
Decision:
0 v$ o& |& p. Z( I( _: w1. It is permitted to demonstrate compliance with Subclause 2.3.2 by means of single fault testing.
$ x l1 D: w0 ~The limits in 2.3.1.b) shall not be exceeded in normal or single fault conditions.
; S, d, x/ p( \5 H; M1 N# y2. Before carrying out single fault testing of components and insulation, insulation between TNV-3 and; g$ E- @ l' R x1 _
SELV circuits not meeting the requirements of Basic insulation should be short circuited if this results in
1 i; h# w# w" Y/ W: p+ Wa worst case voltage measurement at accessible parts of SELV and TNV-1 circuits, and at accessible
9 z: f8 e: T+ k Xconductive parts during subsequent fault testing.% L' k: ~' S% a$ ~. Z2 |: f( G
3. If the single fault test would be more severe if carried out without short circuiting the insulation, the test" `; {7 N/ Y/ c
should be done without short circuiting the insulation.6 Q1 }! i r+ f% }
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