DSH 595 Requirement for the screws fixing internal parts

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DSH 595 + {( h* Z- n# u

Requirement for the screws fixing internal parts

17.3 ! ~* Q& R0 ]( `+ U! Q$ n4 o/ q

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

Standard(s):
) e1 m3 E5 P* U4 R# x+ ?IEC 60065 : 1998 6th edition
! J9 A7 n1 J6 Q+ }7 Q  \9 N' d, SIEC 60065 : 2001 7th edition
5 L# L. z: s7 t8 J8 S7 M$ pSub clause(s):
! o0 r# ~6 f1 Q% o. I17.3
( p9 ?; K2 B" S2 PSheet n.
+ W5 V6 ^& O) y/ R9 f) Z( o) bDSH 595
Subject:
Requirement for the screws fixing
+ l4 b5 @5 z9 X2 d' H( a( E! S! T7 vinternal parts
Key words:
- Screws
; p. }  P, @) ^2 J0 h+ p0 `5 r) Z- Fixing internal parts
Decision approved
during the 44th CTL
meeting 2007
0 N* c6 V( Z" vQuestion: Should those screws, fixing internal parts, needed to be replaced for a service be captive or
# A4 i8 a; u3 P5 s$ o$ R5 g& ycomply 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?
  e+ D) D( {" s; S- Situation
- There is an amplifier which has an internal SMPS board encased by a metal enclosure.
- The screws fixing the internal box should be unscrewed to get serviced.
! a% Q- B  a9 J6 j8 s2 P& R- The screws are inserted from an exterior side or bottom of the amplifier but not fixing the cover of the
amplifier.
- The screws are not captive but don't comply with the insulation distance stated in clause 13 when replaced by
1 l4 J  X2 l5 J: Oother screws having the same nominal diameter with a length of 10 times their nominal diameter.
4 p- k% T9 R) ^Decision
It'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
. B5 k  N  F( C/ p' p5 r$ F5 [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.
6 b5 Z  f- s; L& EIn the above case reinforced insulation is required because after the screws are replaced the amplifier can be
3 ^+ t& {! A. o& I3 p; P$ I- vused without any malfunction.

5 q0 p( r5 H  ]; {