DSH 595 Requirement for the screws fixing internal parts

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DSH 595 ! p4 ~0 f( }( B4 D) `: h1 ~

Requirement for the screws fixing internal parts ) ], d! ?/ _, S; E1 a

17.3

60065(ed.6) & 60065(ed.7)

Standard(s):
" N& h+ H3 ~8 i8 }IEC 60065 : 1998 6th edition
IEC 60065 : 2001 7th edition
8 X6 x' z; V- n, \' c; a; ySub clause(s):
0 P7 `3 a6 ?- V5 P17.3
) W. u1 a# z) \4 L! |# G( HSheet n.
DSH 595
9 j7 H0 y% a1 ~& WSubject:
, {7 l. s5 C; rRequirement for the screws fixing
: T) [5 g: h6 q' N9 H3 V  Winternal parts
Key words:
! }- n2 S& g5 X, |6 x- Screws
- Fixing internal parts
Decision approved
1 y' O; |- T6 x" {" I  I0 J6 E! Lduring the 44th CTL
meeting 2007
8 i; Q; _7 F( R- p* GQuestion: Should those screws, fixing internal parts, needed to be replaced for a service be captive or
& R6 F' W2 e8 X& [comply with the insulation distance stated in clause 13 when replaced by screws having the same nominal
diameter with a length of 10 times their nominal diameter? In the latter case, what insulation is required
between the replaced screws and hazardous live parts?
- Situation
* v( e! @1 {; `7 r$ g: X1 u- There is an amplifier which has an internal SMPS board encased by a metal enclosure.
5 x+ G8 v$ Y5 [) ?* T* h- The screws fixing the internal box should be unscrewed to get serviced.
- The screws are inserted from an exterior side or bottom of the amplifier but not fixing the cover of the
; f2 u( I4 o$ M3 ?8 h5 c! a% }amplifier.
- The screws are not captive but don't comply with the insulation distance stated in clause 13 when replaced by
1 R- y( e( B0 {, q+ G+ y& Lother screws having the same nominal diameter with a length of 10 times their nominal diameter.
+ D* W8 M- Z3 M& vDecision
- U" m( ~, p% |4 I4 F  fIt's not acceptable. In case of a PCB fixed by just screws without any enclosure, it's acceptable because the
service personnel can make sure that the screws are the right screws during a service. However, in case of the
above SMPS board encased by a metal enclosure, it's not acceptable because the service personnel can't know
whether the screws are the right screws or not during a service due to the internal metal enclosure.
: G6 F( `6 @4 wIn the above case reinforced insulation is required because after the screws are replaced the amplifier can be
3 \7 s6 K) }- x0 w! V3 R+ Q- Sused without any malfunction.


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