DSH 595 Requirement for the screws fixing internal parts

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DSH 595 $ R4 ]9 G6 X9 d. U3 t8 c6 _2 m5 a

Requirement for the screws fixing internal parts 6 f( {/ H3 n, Q- G5 `% L% M0 j& I) d

17.3 4 h3 N2 U) P/ ?

60065(ed.6) & 60065(ed.7) 2 ^+ `2 p3 c! y, F# Y

Standard(s):
/ T# g& x9 w. x& Z- n+ t) w  JIEC 60065 : 1998 6th edition
IEC 60065 : 2001 7th edition
0 R, G/ f/ t" `7 S- O0 BSub clause(s):
% H$ |3 O# F, Y9 v/ P5 b17.3
Sheet n.
DSH 595
Subject:
" `8 o, X" l: y) {) c! PRequirement for the screws fixing
internal parts
0 z' ]: p) t7 Z4 `( J: f7 z0 c4 }Key words:
- Screws
- Fixing internal parts
Decision approved
6 }1 x" l3 y8 @) F* ]5 L( `& Z9 s5 G9 fduring the 44th CTL
) A  o  P2 N3 I2 b0 _5 r$ _- f- fmeeting 2007
Question: Should those screws, fixing internal parts, needed to be replaced for a service be captive or
5 x4 y+ p% X6 ]/ w& Y1 d' rcomply with the insulation distance stated in clause 13 when replaced by screws having the same nominal
3 C  A1 i- X7 q/ ?  ?* E( ldiameter 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?
+ Y2 h& D. _5 D+ Q" {8 g/ e- Situation
- There is an amplifier which has an internal SMPS board encased by a metal enclosure.
; o. L+ E  P2 E2 n, x1 [) c( T- The screws fixing the internal box should be unscrewed to get serviced.
: c# ^5 ?7 t  [  l2 f3 ?- The screws are inserted from an exterior side or bottom of the amplifier but not fixing the cover of the
. [4 u2 O. ~3 b1 Bamplifier.
7 ~% ?' x  Y0 m- The screws are not captive but don't comply with the insulation distance stated in clause 13 when replaced by
9 ^" [( g/ Y. z/ ~other screws having the same nominal diameter with a length of 10 times their nominal diameter.
4 H  B7 c( r4 i4 _Decision
2 `7 G) |' [* _  u0 H/ k/ a6 yIt'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
/ f3 B2 g4 s& k. r# Qabove SMPS board encased by a metal enclosure, it's not acceptable because the service personnel can't know
$ c! S/ C  K4 C5 kwhether the screws are the right screws or not during a service due to the internal metal enclosure.
In the above case reinforced insulation is required because after the screws are replaced the amplifier can be
used without any malfunction.
) `. f9 C2 d6 M" j- W$ t) T/ e