Another form of wiring is known as the extended passive bus. In this case the total maximum distance allowed is greater, up to about 500 metres, but there is a restriction on where the devices may be located on the main cable.

The maximum length of the drop cable is the same as before (ten metres). The restriction is that the device nearest the NT1 must be no more than either 25 or 50 metres from the end of the main cable furthest from the NT1. The smaller distance is for 100Ω cable, the larger for 200Ω cable.