As many as eight devices can be connected to a BRI NT1, but the NT1 normally only has two sockets. You must use some special wiring to connect more than two devices and there are also rules about the maximum distances involved.

In this configuration, known as the short passive bus, the devices are randomly distributed along the length of the cable. Each of the drop cables (between the main cable and the device) may be as long as ten metres.

The total length of the main cable may not be longer than either 100 metres or 200 metres, depending on the quality of the cable. Cable has a characteristic impedance, either 100Ω or 200Ω. With the 100Ω cable, the maximum length is 100 metres, whereas with the more expensive 200Ω cable, the maximum length can be 200 metres. The characteristic impedance is usually quoted by the cable supplier.