DSH 376 Backfeed protection

小米

广东安规检测
有限公司提供：

小型摆管淋雨试验机

IPX5X6X7喷水试验机

1000L恒温恒湿箱

各种试验指现货

可程式恒温恒湿试验箱

水平垂直燃烧机

自动卷线器试验机

耐划痕试验机

各种灯头量规现货

灼热丝试验机现货

GB1002插头量规

IPX1-X7淋雨现货

IEC61347/UL935镇流器热试验箱

灯具防风罩

IK冲击试验机

UL498插头插座量规

VDE0620插头插座量规

稳定性试验台

家电温升测试角

针焰试验机现货

热电偶焊机现货

家电125mm试验指

E12灯头量规

无绳壶无绳电熨斗插拔寿命试验机

IEC60335试验指甲

DSH 376 9 n  e) M  I1 w) V: F

Backfeed protection

- 6 `5 n1 Z5 h1 j* i7 }6 v

60950(ed.3) ! c) D* r1 `  g7 ^# G

Standard:
IEC 60950 Ed. 3
: n8 G- S3 l8 f$ o3 x) K6 lSub clause: --- Sheet n. 376
Page 1(1)
; a% h: K8 u. \6 k' mSubject:
Backfeed protection
& I0 l+ P% }8 q/ i& ~Key words:
9 L$ n" f$ B3 ^& E2 U5 w- Backfeed Protection
Decision taken at
37th CTL
meeting/2000 further
* a; t" k  w  jto the trial period
consultation
Question:
The product in question is a power supply to IEC/EN 60950 with an internal Battery Back Up
Unit (BBU). The BBU provides 170Vdc, which is connected to the “output” of the mainsrectifier
bridge. The question is related to the backfeed protection to prevent potential risk of
# b1 ?* G8 ~  h/ r9 welectric shock from being present on the mains supply terminals during interruption of the
primary power or removal of the plugs from its socket.
Different interpretations have been experienced, and we are looking forward to a consensus.
Three alternatives may be listed as follows:
1.
4 X# L3 G8 W0 Z& R  CThe BBU can be considered similar to parts of an Uninterruptible Power Systems (UPS), for
which there is the European standard EN 50091-1. However this standard is not an IEC
standard and may not be applicable outside CENELEC. EN 50091-1 specifies requirements for
2 c1 n! S3 p' J) L9 W. Ibackfeed protection. Sub clause 2.1.5 states that such switching device shall be of an all pole
/ j& U: |: o1 Ntype having an air gap in each pole in accordance with EN 60950 Table 5 – Minimum
clearances in secondary circuits and using the column headed “circuits not subjected to
transient overvoltage” – for reinforced insulation at the working voltage that is backfed (in this
; e/ ^  L4 |( o4 T2 K# P  Acase 170Vdc).
2.
According to sub clause 2.2.6 (IEC 60950), it is likely to apply reinforced insulation between
unearthed hazardous voltage secondary circuit and unearthed accessible parts.
3.
1 w: X  ]& W# |' m2 ~# z- vIf the voltage on the mains plug does not exceed 60Vdc (or 42.2V peak) in the event of a
single failure, when the mains plug is disconnected and the battery provides 170Vdc to the
8 K) r1 ?/ Y& n“output” of the mains rectifier bridge, no additional requirements for “backfeed protection”
& E! L0 t) M7 s' D; s( N8 Ashould be applicable.
Decision:
Interpretation Item 3 is the correct one