All CBus products draw their power from the CAT5 wiring. Wall switches, PIRs, temperatures sensors, etc all have different power requirements measured in milliamps (mA).
If you have already completed a system specification and listed all of the devices you require, you can add up the total power requirement by checking the mA rating of each unit in the CBus product guide (linked to the right).
CBus relay and dimmer units are available in ‘powered’ and ‘non-powered’ versions detailed here. Each powered version you have on your system supplies 200mA to the bus network for powering your other CBus units. There is also a separate power supply available which will supply 350mA.
Let’s say you have a total power requirement of 550mA for your system, then specifying three powered devices (either relays or dimmers) would be sufficient for the system to operate properly.