74/575/INF：IEC 60950-1通信網(wǎng)絡接觸電流的總和

Summation of Leakage (Touch) Current

Questions to the Panel:

5.1.8.2 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.

74/575/INF簡要解析：

ISDN S-BUS電信總線的一拖八（1主機8終端機）的設備適用于5.1.8.2條款規(guī)定“除非已知來自其他設備的實際電流較小，應當假定每個通信端口從其他設備接收的電流為0.25mA”，可以假定最大接觸電流為0.25mA*9，滿足連接到保護接地端子的3.5mA限值（前提是所有互連電路連到一個公共回路點，然后將該點接到保護地上）

USB接口不認為通信網(wǎng)絡的端口，因為標準5.1.8注釋規(guī)定了“通信端口是包括那些預定要附裝通信網(wǎng)絡的連接點。這些通信端口不包括其他數(shù)據(jù)端口，例如通常確定為串行、并行、鍵盤、游戲、操縱桿等的數(shù)據(jù)端口”