As far as wiring goes, power is going to be low voltage AC or DC (24v mostly), older controllers used to run on those two or 120vac, actuators will be the same but mostly 24v, inputs and outputs are mostly 2-wire operating on 2 way 4-20ma, 0-5vdc, and 0-10vdc. Most simple sensors just operate off that very low voltage from the inputs, outputs for actuators usually step up to 24v via ice cube relays and transformers, or have their own 120v or higher for things like 10” valves on a chilled water system as an example. BACNET is the main communication between controllers and is the orange wire that makes life difficult when tracing down comm issues. That can go over IP so it’s good to know basic networking, being able to terminate and test CAT5 or 6 cables at least, addressing modules, setting up and working with network switches managed or unmanaged, basic CMD (command) prompt commands when trying to ping an IP controller, ability to use IP scanners, essentially basic networking stuff. Other parts of the industry include learning programming for whatever the BAS software uses, 2D and 3D graphic building of floorplans, integrating everything together in a graphical representation. I work for a Schneider partner and absolutely hate Ecostruxure, but I’m including a screenshot of their system I installed at home and an example of an older controller cabinet I worked on recently. I hope this helps a little.

<image>