All the data bus modules (keypads, expansion I\O, etc.) use 12vdc power off the data bus, and the main board provides VAUX output power for devices like smoke alarms, as well as its own 12v digital outputs, etc. I’ve seen specs for fusing of different features, but I haven’t seen a spec. for the maximum output capacity as a whole, of the on-board 12v power supply. And what is the spec on maximum 12v draw per data bus? Output expanders have a potential of 330mA each, so two or three along a single bus is drawing a lot of DC power and I assume there’s a maximum capacity for the power delivery per bus line.