74/575/INF:IEC 60950-1通信网络接触电流的总和

2021-10-15 14:07:34

Summation of Leakage (Touch) Current

Questions to the Panel: Summation of leakage (touch) current from telecommunication networks states:

"It shall be assumed that each telecommunication port receives 0,25mA from the other equipment, unless the current is known to be lower."

Is that statement also acceptable for a telecommunication bus system like the ISDN S-bus with 8 terminal equipment? Or as an other common example the USB (Universal Serial Bus) interface in computers?

Opinions of the Panel:

The ISDN S-bus falls within the definition of a TELECOMMUNICATION NETWORK, so that all of subclause 5.1.8 applies. The maximum number of equipments permitted to be connected to the S-bus is nine (eight user terminals plus one), which could lead to a maximum TOUCH CURRENT of 9 x 0,25 mA. This is within the TOUCH CURRENT limit of 3,5 mA in subclause 5.1.6, table 5A.

The USB interface is not considered a TELECOMMUNICATION NETWORK interface, see the 5.1.8 Note making reference to data ports such as serial, parallel, etc. Therefore, the requirements of 5.1.8 are not applied to such bus systems.


ISDN S-BUS电信总线的一拖八(1主机8终端机)的设备适用于5.1.8.2条款规定“除非已知来自其他设备的实际电流较小,应当假定每个通信端口从其他设备接收的电流为0.25mA”,可以假定最大接触电流为0.25mA*9,满足连接到保护接地端子的3.5mA限值(前提是所有互连电路连到一个公共回路点,然后将该点接到保护地上