DSH 595 Requirement for the screws fixing internal parts

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DSH 595 + e; P9 x! ]. h: z, y" c0 O

Requirement for the screws fixing internal parts 8 O( w: r: e9 V) [2 @3 l9 W

17.3

60065(ed.6) & 60065(ed.7) # r4 w+ E9 {6 F: C( _: P

2 f4 V+ X3 F7 ^) GStandard(s):
: _- g" H  D0 wIEC 60065 : 1998 6th edition
( Z( p+ t' [% k6 a- eIEC 60065 : 2001 7th edition
; j; C6 p# ^3 R. lSub clause(s):
# |4 e* T; d% @8 Y5 c. V) D17.3
Sheet n.
) t/ r5 k2 I/ W5 w3 z7 dDSH 595
Subject:
Requirement for the screws fixing
internal parts
' J) C& R/ X) NKey words:
1 _, q  j% T% g8 J" w- Screws
- Fixing internal parts
& j% c" ^/ L: L+ m3 b, vDecision approved
during the 44th CTL
* \( z2 ]6 l3 y5 i2 lmeeting 2007
Question: Should those screws, fixing internal parts, needed to be replaced for a service be captive or
! }; m( Q+ x( S" ?, Y( Wcomply with the insulation distance stated in clause 13 when replaced by screws having the same nominal
* O: r& P4 J1 w; s. B8 e7 idiameter 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?
$ o4 Q$ v/ Q* d' |3 E- 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.
- The screws are inserted from an exterior side or bottom of the amplifier but not fixing the cover of the
1 j$ t/ m# D1 y! L; [amplifier.
- The screws are not captive but don't comply with the insulation distance stated in clause 13 when replaced by
/ _+ h$ t6 v/ B  A% zother screws having the same nominal diameter with a length of 10 times their nominal diameter.
Decision
: y/ |9 v9 H& R) t/ a3 I8 S( V- VIt's not acceptable. In case of a PCB fixed by just screws without any enclosure, it's acceptable because the
# T7 F) ]6 q! R2 v4 Cservice 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.
, }1 n! q% L* W: M/ z$ [In the above case reinforced insulation is required because after the screws are replaced the amplifier can be
used without any malfunction.
) R& ^) W& O! q& x! I