220.127.116.11 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?
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.